Volume Shadowing for OpenVMS

Document revision date: 30 March 2001

Volume Shadowing for OpenVMS

Contents

Index

4.4.1 MOUNT Command Qualifiers Specific to Shadowing

The MOUNT command qualifiers described in Table 4-1 are specific to shadowing.

Table 4-1 MOUNT Command Qualifiers (Shadowing Specific)
Qualifier Function

/[NO]CONFIRM Controls whether the Mount utility issues a request to confirm a copy operation when mounting a shadow set. The default is /NOCONFIRM.

/[NO]COPY Enables or disables copy operations on physical devices named when mounting or adding to a shadow set. The default is /COPY.

/[NO]INCLUDE Automatically mounts and reinstates a shadow set to the way it was before the shadow set was dissolved. The default is /NOINCLUDE.

/OVERRIDE=NO_FORCED_ERROR Directs the Mount utility to proceed with shadowing, even though the device or controller does not support forced error handling. Using unsupported SCSI disks can cause members to be removed from a shadow set if certain error conditions arise that cannot be corrected, because some SCSI disks do not implement READL and WRITEL commands that support disk bad-block repair. If the SCSI device does not support READL and WRITEL commands, the SCSI disk class driver sets a NOFE (no forced error) bit in a System Dump Analyzer display. See Section 4.9.4.1 for more information.

/OVERRIDE=SHADOW_MEMBERSHIP Mounts a former shadow set member and zeroes the disk's shadow set generation number so that the disk is no longer marked as having been a member of the shadow set.

/POLICY= [NO]MINICOPY [=OPTIONAL] Controls the setup and use of the shadowing minicopy function. The meaning of [NO]MINICOPY[=OPTIONAL] depends on the status of the shadow set. If the shadow set is not mounted, either on a standalone system or on any cluster member, and MINICOPY=OPTIONAL is specified, the shadow set is mounted and a write bitmap is created. (A write bitmap enables a shadowing minicopy operation.) MOUNT/POLICY=MINICOPY[=OPTIONAL] must be specified on the initial mount of a shadow set, either on a standalone system or in a cluster, to enable the shadowing minicopy operation.
The OPTIONAL keyword allows the mount to continue, even if the system was unable to start the write bitmap. A bitmap could fail to start properly because of an improperly dismounted shadow set, a shadow set that requires a merge operation, or various resource problems. If the OPTIONAL keyword is omitted and the system is unable to start the write bitmap, the shadow set will not be mounted.
If you specify /POLICY=MINICOPY=OPTIONAL and the shadow set was already mounted on another node in the cluster without this qualifier and keyword, the MOUNT command will succeed but a write bitmap will not be created.
If NOMINICOPY is specified, the shadow set will be mounted but a write bitmap will not be created.
If a former member of the the shadow set is returned to the shadow set, which has minicopy enabled, then a minicopy is started instead of a full copy. This is the default behavior and will occur even if you omit /POLICY=MINICOPY[=OPTIONAL]. If a minicopy successfully starts and then fails for some reason, a full copy will be performed.
If a minicopy cannot be started and the keyword OPTIONAL was omitted, the mount will fail.
If NOMINICOPY is specified, then a minicopy will not be performed, even if one is possible.

/POLICY=REQUIRE_MEMBERS Controls whether every physical device specified with the /SHADOW qualifier must be accessible when the MOUNT command is issued in order for the MOUNT command to take effect. The proposed members are either specified in the command line or found on the disk by means of the /INCLUDE qualifier. The default behavior is that if one or more members is not accessible for any reason (such as a connectivity failure), then the virtual unit will be created with the remaining members. This option is especially useful in disaster-tolerant clusters because it ensures that the correct member is selected as the master member after an event.

/POLICY=VERIFY_LABEL Requires that any member to be added to the shadow set have a volume label of SCRATCH_DISK.
This helps ensure that the wrong disk is not added to a shadow set by mistake. If you plan to use VERIFY_LABEL, then before using this qualifier you must either initialize the disk to be added to the set with the label SCRATCH_DISK, or specify a label for the disk with the command SET VOLUME/LABEL.
The default behavior is NOVERIFY_LABEL, which means that the volume label of the copy targets will not be checked. This is the same behavior that occurred before the introduction of this qualifier. The volume label of the copy targets will not be checked.

/SHADOW=( physical-device-name[:][,...]) Directs the Mount utility to bind the specified physical devices into a shadow set represented by the virtual unit named in the command.

**Table 4-1 MOUNT Command Qualifiers (Shadowing Specific)**
Qualifier	Function
/[NO]CONFIRM	Controls whether the Mount utility issues a request to confirm a copy operation when mounting a shadow set. The default is /NOCONFIRM.
/[NO]COPY	Enables or disables copy operations on physical devices named when mounting or adding to a shadow set. The default is /COPY.
/[NO]INCLUDE	Automatically mounts and reinstates a shadow set to the way it was before the shadow set was dissolved. The default is /NOINCLUDE.
/OVERRIDE=NO_FORCED_ERROR	Directs the Mount utility to proceed with shadowing, even though the device or controller does not support forced error handling. Using unsupported SCSI disks can cause members to be removed from a shadow set if certain error conditions arise that cannot be corrected, because some SCSI disks do not implement READL and WRITEL commands that support disk bad-block repair. If the SCSI device does not support READL and WRITEL commands, the SCSI disk class driver sets a NOFE (no forced error) bit in a System Dump Analyzer display. See Section 4.9.4.1 for more information.
/OVERRIDE=SHADOW_MEMBERSHIP	Mounts a former shadow set member and zeroes the disk's shadow set generation number so that the disk is no longer marked as having been a member of the shadow set.
/POLICY= [NO]MINICOPY [=OPTIONAL]	Controls the setup and use of the shadowing minicopy function. The meaning of [NO]MINICOPY[=OPTIONAL] depends on the status of the shadow set. If the shadow set is not mounted, either on a standalone system or on any cluster member, and MINICOPY=OPTIONAL is specified, the shadow set is mounted and a write bitmap is created. (A write bitmap enables a shadowing minicopy operation.) MOUNT/POLICY=MINICOPY[=OPTIONAL] must be specified on the initial mount of a shadow set, either on a standalone system or in a cluster, to enable the shadowing minicopy operation. The OPTIONAL keyword allows the mount to continue, even if the system was unable to start the write bitmap. A bitmap could fail to start properly because of an improperly dismounted shadow set, a shadow set that requires a merge operation, or various resource problems. If the OPTIONAL keyword is omitted and the system is unable to start the write bitmap, the shadow set will not be mounted. If you specify /POLICY=MINICOPY=OPTIONAL and the shadow set was already mounted on another node in the cluster without this qualifier and keyword, the MOUNT command will succeed but a write bitmap will not be created. If NOMINICOPY is specified, the shadow set will be mounted but a write bitmap will not be created. If a former member of the the shadow set is returned to the shadow set, which has minicopy enabled, then a minicopy is started instead of a full copy. This is the default behavior and will occur even if you omit /POLICY=MINICOPY[=OPTIONAL]. If a minicopy successfully starts and then fails for some reason, a full copy will be performed. If a minicopy cannot be started and the keyword OPTIONAL was omitted, the mount will fail. If NOMINICOPY is specified, then a minicopy will not be performed, even if one is possible.
/POLICY=REQUIRE_MEMBERS	Controls whether every physical device specified with the /SHADOW qualifier must be accessible when the MOUNT command is issued in order for the MOUNT command to take effect. The proposed members are either specified in the command line or found on the disk by means of the /INCLUDE qualifier. The default behavior is that if one or more members is not accessible for any reason (such as a connectivity failure), then the virtual unit will be created with the remaining members. This option is especially useful in disaster-tolerant clusters because it ensures that the correct member is selected as the master member after an event.
/POLICY=VERIFY_LABEL	Requires that any member to be added to the shadow set have a volume label of SCRATCH_DISK. This helps ensure that the wrong disk is not added to a shadow set by mistake. If you plan to use VERIFY_LABEL, then before using this qualifier you must either initialize the disk to be added to the set with the label SCRATCH_DISK, or specify a label for the disk with the command SET VOLUME/LABEL. The default behavior is NOVERIFY_LABEL, which means that the volume label of the copy targets will not be checked. This is the same behavior that occurred before the introduction of this qualifier. The volume label of the copy targets will not be checked.
/SHADOW=( physical-device-name[:][,...])	Directs the Mount utility to bind the specified physical devices into a shadow set represented by the virtual unit named in the command.

Caution

Do not use the /OVERRIDE=IDENTIFICATION or /NOMOUNT_VERIFICATION qualifiers when mounting shadow sets. Using either of these qualifiers can result in loss of data.

If you mount a shadow set with the /OVERRIDE=IDENTIFICATION qualifier, individual shadow set members start with different volume labels, which can cause a volume to lose data.

If you specify the /NOMOUNT_VERIFICATION qualifier, the shadow set becomes unusable at the first state change of the shadow set.

4.4.2 Additional MOUNT Command Qualifiers Used for Shadowing

The MOUNT command qualifiers described in this section are not specific to shadowing but can be very useful when creating shadow sets. These additional qualifiers are described in Table 4-2 and in the examples that follow.

Table 4-2 Additional MOUNT Command Qualifiers (Not Shadowing Specific)
Qualifier Function

/NOASSIST Successfully mounts a shadow set if at least one of the devices included in the MOUNT command is available for mounting. If the command does not include the /NOASSIST qualifier, and a device included in the MOUNT command is not available for mounting, the MOUNT command will mount the shadow set.

/SYSTEM Makes the volume available to all users on the system. Use this qualifier when you add a disk to an existing shadow set. If the /CLUSTER qualifier was used when the shadow set was created, the use of /SYSTEM will make the new member of the shadow set available to all nodes in the cluster that already have the shadow set mounted.

/GROUP Makes the volume available to all users with the same group number in their UICs as the user entering the MOUNT command. You must have GRPNAM and SYSNAM user privileges to mount group and system volumes.

/CLUSTER Creates the virtual unit automatically on every node in the cluster on which shadowing is enabled. Use this qualifier if the shadow set is to be accessed across the cluster. You must have the SYSNAM privilege to use this qualifier. Using /CLUSTER automatically includes the /SYSTEM qualifier, making the shadow set available to all users on the system.

**Table 4-2 Additional MOUNT Command Qualifiers (Not Shadowing Specific)**
Qualifier	Function
/NOASSIST	Successfully mounts a shadow set if at least one of the devices included in the MOUNT command is available for mounting. If the command does not include the /NOASSIST qualifier, and a device included in the MOUNT command is not available for mounting, the MOUNT command will mount the shadow set.
/SYSTEM	Makes the volume available to all users on the system. Use this qualifier when you add a disk to an existing shadow set. If the /CLUSTER qualifier was used when the shadow set was created, the use of /SYSTEM will make the new member of the shadow set available to all nodes in the cluster that already have the shadow set mounted.
/GROUP	Makes the volume available to all users with the same group number in their UICs as the user entering the MOUNT command. You must have GRPNAM and SYSNAM user privileges to mount group and system volumes.
/CLUSTER	Creates the virtual unit automatically on every node in the cluster on which shadowing is enabled. Use this qualifier if the shadow set is to be accessed across the cluster. You must have the SYSNAM privilege to use this qualifier. Using /CLUSTER automatically includes the /SYSTEM qualifier, making the shadow set available to all users on the system.

4.4.3 Creating a Shadow Set With /NOASSIST

You may occasionally find it useful to specify the /NOASSIST qualifier on the MOUNT command. For example, you can use the MOUNT/NOASSIST command in startup files to avoid failure of a MOUNT command when a device you specify in the command is not available. The /NOASSIST qualifier can be used in startup files because operator intervention is impossible during startup.

The MOUNT/NOASSIST qualifier can successfully mount the shadow set as long as at least one of the devices included in the MOUNT command is available for mounting. Example 4-2 shows an example of the /NOASSIST qualifier and the resulting messages when one of the members included in the command is not available for mounting.

Example 4-2 Using the /NOASSIST Qualifier

$ MOUNT/SYS DSA65:/SHADOW=($4$DIA6,$4$DIA5) GALEXY/NOASSIST %MOUNT-I-MOUNTED, GALEXY mounted on _DSA65: %MOUNT-I-SHDWMEMSUCC, _$4$DIA6: (READY) is now a valid member of the shadowset %MOUNT-I-SHDWMEMFAIL, $4$DIA5 failed as a member of the shadow set -SYSTEM-F-VOLINV, volume is not software enabled

Even though device $4$DIA5 is not available for mounting, the MOUNT command continues to create the shadow set with $4$DIA6 as its only member. If the command did not include the /NOASSIST qualifier, the MOUNT command would not mount the shadow set.

4.4.4 Creating a Shadow Set With /SYSTEM and With /CLUSTER

When you create a shadow set, you must specify either the /SYSTEM qualifier or the /CLUSTER qualifier, or both (see Table 4-2) to provide access for all users on a single system or on a cluster.

In Example 4-3, if the shadow set (identified by its virtual unit name DSA2 ) is not currently mounted, the first command creates a shadow set with one shadow set member; the second command adds two more members to the same shadow set. An automatic copy operation causes any data on the second and third volumes to be overwritten as the shadow set members are added.

In the second MOUNT command, you need only specify the /SYSTEM when you add the $6$DIA5 and $6$DIA6 devices to the shadow set. Do not use /CLUSTER. These disks are added with the same status that the shadow set currently has, which in this case is clusterwide access.

Example 4-3 Using the /CLUSTER Qualifier

$ MOUNT DSA2: /CLUSTER /SHADOW=$6$DIA4: PEAKSISLAND DISK$PEAKSISLAND $ MOUNT DSA2: /SYSTEM/SHADOW=($6$DIA5:,$6$DIA6:) PEAKSISLAND DISK$PEAKSISLAND

4.5 Adding Shadow Set Members

Once a shadow set is created, you can add and remove individual members by mounting or dismounting physical disk devices. The shadowing software allows you to add and remove shadow set members at any time, transparently to user processes or applications running on the system.

4.5.1 Adding a Disk to an Existing Shadow Set

Example 4-4 shows how to add the disk $4$DUA3 to the DSA23 shadow set.

Example 4-4 Adding a Disk to an Existing Shadow Set

$ MOUNT/CONFIRM/SYSTEM DSA23: /SHADOW=($4$DUA9,$4$DUA3) volume-label

The command in Example 4-4 specifies both the currently active shadow set member ($4$DUA9) and the new member ($4$DUA3). Although it is not necessary to include them when mounting additional physical devices, you can specify current shadow set members without affecting their membership state.

Note that when you add volumes to an existing shadow set mounted across an OpenVMS Cluster system, the shadowing software automatically adds the new members on each OpenVMS Cluster node.

4.5.2 Creating a Two-Member Shadow Set and Adding a Third Member

Example 4-5 shows two commands. The first command creates the shadow set with two members; the next adds a third member to that shadow set.

Example 4-5 Creating a Shadow Set and Adding Third Member

$ MOUNT/SYSTEM DSA4: /SHADOW = ($3$DIA7:, $3$DIA8:) FORMERSELF(1) %MOUNT-I-MOUNTED, FORMERSELF mounted on DSA4: %MOUNT-I-SHDWMEMSUCC, _$3$DIA7: (DISK300) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$3$DIA8: (DISK301) is now a valid member of the shadow set $ MOUNT/SYSTEM DSA4: /SHADOW = $3$DIA6: FORMERSELF(2) %MOUNT-I-SHDWMEMCOPY, _$3$DIA6: (DISK302) added to the shadow set with a copy operation

A shadow set is created whose virtual unit name is DSA4. The member disks are $3$DIA7 and $3DIA8.
The disk $3$DIA6 is mounted systemwide in the shadow set identified by virtual unit DSA4. The shadow set now includes three shadow set members: $3$DIA6, $3$DIA7, and $3$DIA8. In this example, when you add $3$DIA6 after the shadow set already exists, the added volume becomes the target of a copy operation.

4.5.3 Checking Status of Potential Shadow Set Members With /CONFIRM

When you add a disk to an existing shadow set, a copy operation is necessary. Volume shadowing automatically performs the copy operation, unless you use the /CONFIRM qualifier or the /NOCOPY qualifier. When you specify the /CONFIRM qualifier, as shown in Example 4-6, the MOUNT command displays the targets of copy operations and requests permission before the operations are performed. This precaution prevents the erasing important data. For more information about copy operations, see Chapter 6.

Example 4-6 Using the /CONFIRM Qualifier

$ MOUNT/CONFIRM DSA23: /SHADOW=($1$DUA4:,$1$DUA6:) SHADOWVOL (1) %MOUNT-F-SHDWCOPYREQ, shadow copy required Virtual Unit - DSA23 Volume Label - SHADOWVOL (2) Member Volume Label Owner UIC (3) $1$DUA6: (LOVE) SCRATCH [100,100] Allow FULL shadow copy on the above member(s)? [N]: NO (4) $

This command instructs MOUNT to build a shadow set with the specified devices and to prompt for permission to perform any copy operations.
Because a copy operation is necessary, the virtual unit name and the volume label are displayed.
The display also includes the physical device name, the volume label, and the volume owner of the potential shadow set member that requires the copy operation.
A response of No causes MOUNT to quit without mounting or copying.

4.5.4 Checking Status of Potential Shadow Set Members With /NOCOPY

When you specify more than one disk, the shadowing software automatically determines the correct copy operation to perform in order to make shadow set members consistent with each other (see Section 6.2 for details). The Mount utility interprets information recorded on each member to determine whether a member requires a copy operation, a merge operation, or no copy operation. If you are not sure which disks might be targets of copy operations, you can specify the /CONFIRM qualifier or the /NOCOPY qualifier as a precaution against overwriting important data when you mount a disk. With the /NOCOPY qualifier, you disable the copy operation.

Example 4-7 shows how to use the /NOCOPY qualifier to check the status of potential shadow set members before any data is erased.

Example 4-7 Using the /NOCOPY Qualifier

$ MOUNT/NOCOPY DSA2: /SHADOW=($1$DUA4:,$1$DUA6:,$1$DUA7:) - _$ SHADOWVOL DISK$SHADOWVOL (1) %MOUNT-F-SHDWCOPYREQ, shadow copy required %MOUNT-I-SHDWMEMFAIL, DUA7: failed as a member of the shadow set %MOUNT-F-SHDWCOPYREQ, shadow copy required (2) $ MOUNT/COPY(3) DSA2: /SHADOW=($1$DUA4:,$1$DUA6:,$1$DUA7:) - _$ SHADOWVOL DISK$SHADOWVOL %MOUNT-I-MOUNTED, SHADOWVOL mounted on _DSA2: %MOUNT-I-SHDWMEMSUCC, _$1$DUA4: (VOLUME001) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$1$DUA6: (VOLUME002) is now a valid member of the shadow set %MOUNT-I-SHDWMEMCOPY, _$1$DUA7: (VOLUME003) added to the shadow set with a copy operation (4)

This command instructs MOUNT to build a shadow set, with the specified devices, but only if a copy or merge operation is not required.
MOUNT did not build the shadow set because the specified disk, loaded on device $1$DUA7, required a copy operation. At this point you can verify that the volume in device $1$DUA7 does not contain any useful data.
If the device does not contain valuable data, you can reenter the MOUNT command and include the /COPY qualifier. This command instructs MOUNT to mount a shadow set and to proceed with the necessary copy or merge operation.
The shadow set is successfully mounted. The $1$DUA7 device is currently the target of a copy operation; it will attain full shadow set membership when the copy operation completes.

4.6 Mounting a Shadow Set on Other Nodes in the Cluster

If a shadow set is already mounted on one or more nodes in an OpenVMS Cluster system, the /SHADOW qualifier is not required when you mount the same shadow set on other nodes in the cluster. For example, if DSA42 is already mounted in the cluster when a new node is brought into the cluster, you can use the following command to mount DSA42 on the new node:

$ MOUNT/SYS DSA42: volume-label logical-name

Upon receiving this command, the volume shadowing software creates the virtual unit on the new node with the same members that currently exist in the cluster.

4.6.1 Reconstructing a Shadow Set With /INCLUDE

Example 4-8 shows how to reconstruct a shadow set. The volume shadowing software determines which disk volumes are former members of the shadow set.

Example 4-8 Reconstructing Shadow Sets With /INCLUDE

$ MOUNT /SYSTEM DSA4/SHAD=($4$DIA1,$4$DIA2,$4$DIA3) NEWDISK(1) %MOUNT-I-MOUNTED, NEWDISK mounted on _DSA4: %MOUNT-I-SHDWMEMSUCC, _$4$DIA1: (DISK01) is now a valid member of the shadow set %MOUNT-I-SHDWMEMCOPY, _$4$DIA2: (DISK02) added to the shadow set with a copy operation %MOUNT-I-SHDWMEMCOPY, _$4$DIA3: (DISK03) added to the shadow set with a copy operation $ DISMOUNT DSA4(2) $ $ MOUNT DSA4:/SYSTEM/SHAD=$4$DIA1 NEWDISK/INCLUDE(3) %MOUNT-I-MOUNTED, NEWDISK mounted on _DSA4: %MOUNT-I-SHDWMEMSUCC, _$4$DIA1: (DISK01) is now a valid member (4) of the shadow set %MOUNT-I-AUTOMEMCOPY, _$4$DIA2: (DISK02) automatically added (4) to the shadow set %MOUNT-I-AUTOMEMCOPY, _$4$DIA3: (DISK03) automatically added (4) to the shadow set

This is the original MOUNT command that created the shadow set represented by DSA4. The shadow set consists of three shadow set members: $4$DIA1, $4$DIA2, and $4$DIA3.
After all copy operations have completed, the DISMOUNT command dissolves the shadow set.
The /INCLUDE qualifier triggers the MOUNT command to reconstruct the shadow set back to the way it was before the shadow set was dissolved. The MOUNT command must specify the original virtual unit name (DSA4) and at least one of the original shadow set members ($4$DIA1). The Mount utility reads the membership list on $4$DIA1 (specified in the MOUNT command) to determine that $4$DIA2 and $4$DIA3 are also members of the shadow set.
Because the shadow set was properly dismounted, the shadow set members are in a consistent state. The MOUNT status messages indicate that the shadow set devices are added back into the shadow set without the need for copy operations.

4.6.2 Mounting a Former Shadow Set Member as a Nonshadowed Disk

Occasionally, you will need to mount a physical shadow set member as a nonshadowed disk. By default, when a shadow set member is mounted outside a shadow set, the Mount utility automatically write-locks the disk. This provides a safeguard against accidental modification, thereby allowing the disk to be remounted into a shadow set at a later time.

To override this default behavior, include the /OVERRIDE=SHADOW_MEMBERSHIP qualifier on the MOUNT command as shown in the following example:

$ MOUNT/OVERRIDE=SHADOW_MEMBERSHIP $4$DUA20: WORKDISK

This command ignores shadow set membership status and mounts a former shadow set member on $4$DUA20 as a nonshadowed disk with write access.

4.7 Specifying Disaster-Tolerant Management Attributes (Alpha Only)

Starting with OpenVMS Alpha Version 7.3, qualifiers to the DCL command SET DEVICE are provided for specifying management attributes for shadow set members located at different sites. By using these qualifiers, system managers can override the default volume shadowing actions that can occur when the systems at one site of a disaster-tolerant OpenVMS Cluster configuration fail. These qualifiers are designed primarily for use in a configuration that uses Fibre Channel for a site-to-site storage interconnect. They can be used in other configurations as well.

Similarly, the DCL command DISMOUNT has been enhanced by the addition of the qualifier /FORCE_REMOVAL ddcu:. This qualifier has been added for the same purpose---to give system managers greater control of shadow set members located at different sites. For more information about this qualifier, see Section 4.8.1.

Table 4-3 SET DEVICE Command Qualifiers for Multiple-Site Shadow Set Members
Qualifier Function

/FORCE_REMOVAL ddcu: If connectivity to a device has been lost and the shadow set is in mount verification, this qualifier causes the member to be expelled from the shadow set immediately.
If the shadow set is not currently in mount verification, no immediate action is taken. If connectivity to a device has been lost but the shadow set is not in mount verification, this qualifier lets you flag the member to be expelled from the shadow set, as soon as it does enter mount verification. The device specified must be a member of a shadow set that is mounted on the node where the command is issued.

/MEMBER_TIMEOUT = xxxxxx ddcu: Specifies the timeout value to be used for a member of a shadow set.
The value supplied by this qualifier overrides the SYSGEN parameter SHADOW_MBR_TMO for this specific device. Each member of a shadow set can be assigned a different MEMBER_TIMEOUT value.
The valid range for xxxxxx is 1 to 16,777,215 seconds.
The device specified must be a member of a shadow set that is mounted on the node where the command is issued.
After you have applied this qualifier to a member, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again.

/MVTIMEOUT = yyyyyy DSA nnnn: Specifies the mount verification timeout value to be used for this shadow set, specified by its virtual unit name, DSA nnnn.
The value supplied by this qualifier overrides the SYSGEN parameter MVTIMEOUT for this specific shadow set.
The valid range for yyyyyy is 1 to 16,777,215 seconds. The device specified must be a shadow set that is mounted on the node where the command is issued.
After you have applied this qualifier, the setting remains in effect as long as the shadow set is mounted. If the shadow set is dismounted and later remounted, this qualifier must be specified again

/READ_COST = zzz ddcu: The valid range for zzz is 1 to 65,535 units.
The device specified must be a member of a shadow set that is mounted on the node where the command is issued.
This qualifier enables you to modify the default "cost" assigned to each member of a shadow set. By modifying the assignments, you can bias the reads in favor of one member of a two-member shadow set, or, in the case of three-member shadow sets, in favor of one or two members of the set over the remaining members.
The shadowing driver assigns default READ_COST values to shadow set members when each member is initially mounted. The default value depends on the device type and its configuration relative to the system mounting it. There are default values for a DECRAM device; a directly connected device in the same physical location; a directly connected device in a remote location; a DECram served device; and a default value for other served devices.
The value supplied by this qualifier overrides the default assignment. The shadowing driver adds the value of the current queue depth of the shadow set member to the READ_COST value and then reads from the member with the lowest value.
After you have applied this qualifier to a member, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again.
Different systems in the cluster can assign different costs to each shadow set member.
If the /SITE command qualifier has been specified, the shadowing driver will take site values into account when it assigns default READ_COST values. Note that in order for the shadowing software to determine whether a device is in the category of "directly connected device in a remote location," the /SITE command qualifier must have been applied to both the shadow set and the DSA device.
Reads requested for a shadow set from a system at site 1 are performed from a shadow set member that is also at site 1. Reads requested for the same shadow set from site 2 can read from the member located at site 2.

/READ_COST = y DSA nnnn The valid range for y is any nonzero number. The value supplied has no inherent meaning. The purpose of this qualifier is to switch the read cost setting for all shadow set members back to the default read cost settings established automatically by the shadowing software. DSA nnnn must be a shadow set that is mounted on the node from which this command is issued.

/SITE = ( nnn, logical_name) ( ddcu: DSA nnnn:) This qualifier indicates to the shadowing driver the site location of the shadow set member or of the shadow set (represented by its virtual unit name). Prior to using this qualifier, you can define the site location in the SYLOGICALS.COM command procedure to simplify its use.
The valid range for nnn is 1 through 255.
After you have applied this qualifier, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again
The following example shows the site locations defined, followed by the use of the /SITE qualifier:
$ DEFINE/SYSTEM/EXEC ZKO 1
$ DEFINE/SYSTEM/EXEC LKG 2
$!
$! At the ZKO site ...
$ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0:,$1$DGA1:) TEST
$ SET DEVICE/SITE=ZKO DSA0:
$!
$! At the LKG site ...
$ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0,$1$DGA1) TEST
$ SET DEVICE/SITE=LKG DSA0:
$!
$! At both sites, the following would be used:
$ SET DEVICE/SITE=ZKO $1$DGA0:
$ SET DEVICE/SITE=LKG $1$DGA1:

/COPY_SOURCE ( ddcu:, DSA nnnn:) Controls whether one or both source members of a shadow set are used as the source for read data during full copy operations, when a third member is added to the shadow set. This only affects copy operations that do not use DCD operations.
HSG80 controllers have a read-ahead cache, which significantly improves single-disk read performance. Copy operations normally alternate reads between the two source members, which effectively nullifies the benefits of the read-ahead cache. This qualifier lets you force all reads from a single source member for a copy operation.
If the shadow set is specified, then all reads for full copy operations will be performed from whichever disk is the current "master" member, regardless of physical location of the disk.
If a member of the shadow set is specified, then that member will be used as the source of all copy operations. This allows you to choose a local source member, rather than a remote master member.

/ABORT_VIRTUAL_UNIT DSA nnnn: To use this qualifier, the shadow set must be in mount verification. When you specify this qualifier, the shadow set aborts mount verification immediately on the node from which the qualifier is issued. This qualifier is intended to be used when it is known that the unit cannot be recovered. Note that after this command completes, the shadow set must still be dismounted. Use the following command to dismount the shadow set:
$ DISMOUNT/ABORT DSA nnnn

**Table 4-3 SET DEVICE Command Qualifiers for Multiple-Site Shadow Set Members**
Qualifier	Function
/FORCE_REMOVAL ddcu:	If connectivity to a device has been lost and the shadow set is in mount verification, this qualifier causes the member to be expelled from the shadow set immediately. If the shadow set is not currently in mount verification, no immediate action is taken. If connectivity to a device has been lost but the shadow set is not in mount verification, this qualifier lets you flag the member to be expelled from the shadow set, as soon as it does enter mount verification. The device specified must be a member of a shadow set that is mounted on the node where the command is issued.
/MEMBER_TIMEOUT = xxxxxx ddcu:	Specifies the timeout value to be used for a member of a shadow set. The value supplied by this qualifier overrides the SYSGEN parameter SHADOW_MBR_TMO for this specific device. Each member of a shadow set can be assigned a different MEMBER_TIMEOUT value. The valid range for xxxxxx is 1 to 16,777,215 seconds. The device specified must be a member of a shadow set that is mounted on the node where the command is issued. After you have applied this qualifier to a member, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again.
/MVTIMEOUT = yyyyyy DSA nnnn:	Specifies the mount verification timeout value to be used for this shadow set, specified by its virtual unit name, DSA nnnn. The value supplied by this qualifier overrides the SYSGEN parameter MVTIMEOUT for this specific shadow set. The valid range for yyyyyy is 1 to 16,777,215 seconds. The device specified must be a shadow set that is mounted on the node where the command is issued. After you have applied this qualifier, the setting remains in effect as long as the shadow set is mounted. If the shadow set is dismounted and later remounted, this qualifier must be specified again
/READ_COST = zzz ddcu:	The valid range for zzz is 1 to 65,535 units. The device specified must be a member of a shadow set that is mounted on the node where the command is issued. This qualifier enables you to modify the default "cost" assigned to each member of a shadow set. By modifying the assignments, you can bias the reads in favor of one member of a two-member shadow set, or, in the case of three-member shadow sets, in favor of one or two members of the set over the remaining members. The shadowing driver assigns default READ_COST values to shadow set members when each member is initially mounted. The default value depends on the device type and its configuration relative to the system mounting it. There are default values for a DECRAM device; a directly connected device in the same physical location; a directly connected device in a remote location; a DECram served device; and a default value for other served devices. The value supplied by this qualifier overrides the default assignment. The shadowing driver adds the value of the current queue depth of the shadow set member to the READ_COST value and then reads from the member with the lowest value. After you have applied this qualifier to a member, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again. Different systems in the cluster can assign different costs to each shadow set member. If the /SITE command qualifier has been specified, the shadowing driver will take site values into account when it assigns default READ_COST values. Note that in order for the shadowing software to determine whether a device is in the category of "directly connected device in a remote location," the /SITE command qualifier must have been applied to both the shadow set and the DSA device. Reads requested for a shadow set from a system at site 1 are performed from a shadow set member that is also at site 1. Reads requested for the same shadow set from site 2 can read from the member located at site 2.
/READ_COST = y DSA nnnn	The valid range for y is any nonzero number. The value supplied has no inherent meaning. The purpose of this qualifier is to switch the read cost setting for all shadow set members back to the default read cost settings established automatically by the shadowing software. DSA nnnn must be a shadow set that is mounted on the node from which this command is issued.
/SITE = ( nnn, logical_name) ( ddcu: DSA nnnn:)	This qualifier indicates to the shadowing driver the site location of the shadow set member or of the shadow set (represented by its virtual unit name). Prior to using this qualifier, you can define the site location in the SYLOGICALS.COM command procedure to simplify its use. The valid range for nnn is 1 through 255. After you have applied this qualifier, the setting remains in effect as long as the member is part of the shadow set. If the member is removed from the shadow set and later returned, this qualifier must be specified again The following example shows the site locations defined, followed by the use of the /SITE qualifier: $ DEFINE/SYSTEM/EXEC ZKO 1 $ DEFINE/SYSTEM/EXEC LKG 2 $! $! At the ZKO site ... $ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0:,$1$DGA1:) TEST $ SET DEVICE/SITE=ZKO DSA0: $! $! At the LKG site ... $ MOUNT/SYSTEM DSA0/SHAD=($1$DGA0,$1$DGA1) TEST $ SET DEVICE/SITE=LKG DSA0: $! $! At both sites, the following would be used: $ SET DEVICE/SITE=ZKO $1$DGA0: $ SET DEVICE/SITE=LKG $1$DGA1:
/COPY_SOURCE ( ddcu:, DSA nnnn:)	Controls whether one or both source members of a shadow set are used as the source for read data during full copy operations, when a third member is added to the shadow set. This only affects copy operations that do not use DCD operations. HSG80 controllers have a read-ahead cache, which significantly improves single-disk read performance. Copy operations normally alternate reads between the two source members, which effectively nullifies the benefits of the read-ahead cache. This qualifier lets you force all reads from a single source member for a copy operation. If the shadow set is specified, then all reads for full copy operations will be performed from whichever disk is the current "master" member, regardless of physical location of the disk. If a member of the shadow set is specified, then that member will be used as the source of all copy operations. This allows you to choose a local source member, rather than a remote master member.
/ABORT_VIRTUAL_UNIT DSA nnnn:	To use this qualifier, the shadow set must be in mount verification. When you specify this qualifier, the shadow set aborts mount verification immediately on the node from which the qualifier is issued. This qualifier is intended to be used when it is known that the unit cannot be recovered. Note that after this command completes, the shadow set must still be dismounted. Use the following command to dismount the shadow set: $ DISMOUNT/ABORT DSA nnnn

Contents

Index

privacy and legal statement

5423PRO_004.HTML