Document revision date: 15 July 2002

Compaq RAID Software for OpenVMS provides ways to configure and use disk drives so that they achieve improved I/O performance. RAID (redundant arrays of independent disks) uses striping technology to chunk data and distribute it across multiple drives. RAID software is available in various levels, one of which is volume shadowing. Table 9-1 describes RAID levels.

Table 9-1 RAID Levels

RAID Level	Description
Level 0	Striping with no redundancy.
Level 1	Shadowing.
Levels 0 + 1	Striping and shadowing together.
Level 3	Striped data with dedicated parity drive. Drives are rotationally synchronized.
Level 5	Striped data and parity.
Level 6	Striped data and parity with two parity drives.

Shadowing striped drives can increase both performance and availability, because you can achieve faster response time with striping and data redundancy with shadowing. In addition to shadowing striped sets, you can also stripe shadow sets. Each strategy offers different advantages and tradeoffs in terms of availability, performance, and cost.

For the latest information about Compaq RAID Software for OpenVMS, refer to the OpenVMS Products page of the Compaq OpenVMS web site:

http://www.openvms.compaq.com

This appendix lists volume shadowing status messages that are displayed on the console device. For other system messages that are related to volume shadowing, use the Help Message utility. For information about the HELP/MESSAGE command and qualifiers, see DCL help (type HELP HELP/MESSAGE at the DCL prompt). Messages that can occur before a system is fully functional are also included in OpenVMS System Messages: Companion Guide for Help Message Users.

A.1 Mount Verification Messages

The following mount verification messages have approximately the same meaning for shadow sets as they do for regular disks. They are sent to the system console (OPA0) and to any operator terminals that are enabled to receive disk operator messages.

• virtual-unit: is off line. Mount verification in progress.
• virtual-unit: has completed mount verification.
• virtual-unit: has aborted mount verification.

The following OPCOM message is returned in response to shadow set operations. This message results when the shadowing code detects that the boot device is no longer in the system disk shadow set. If the boot device is not added back into the system disk shadow set, the system may not reboot, and the dump may be lost if the system crashes.

virtual-unit: does not contain the member named to VMB. System may not reboot.
Explanation: This message can occur for the following reasons:

• The boot device is dismounted or failed out of the system disk shadow set.
• Shadowing finds the boot device missing from the system disk shadow set membership during any dismount operations on the system disk.

• Mount the boot device back into the shadow set as soon as possible.
• If you cannot mount the boot device back into the shadow set, change the device name in VMB (primary bootstrap) so the system can reboot when necessary.

Shadow server operations can display the following status messages on the system console (OPA0) and on terminals enabled to receive operator messages.

Shadow server messages are always informational messages and include the prefix %SHADOW_SERVER-I-SSRVmessage-abbreviation. The following example includes the OPCOM banner and the shadow server message to illustrate what the messages look like when they are output to the console:

%%%%%%%%%%% OPCOM 24-MAR-1990 15:01:30.99 %%%%%%%%%%% (from node SYSTMX at 24-MAR-1990 15:01:31.36) Message from user SYSTEM on SYSTMX %SHADOW_SERVER-I-SSRVINICOMP, shadow server has completed initialization.

The following messages are returned by the shadow server in response to shadow set operations. Several of the messages refer to a copy thread number; this is a unique identifier denoting a copy or merge operation. The messages in this section are listed in alphabetical order by message abbreviation. For simplicity, the messages shown here do not include the SHADOW_SERVER-I- prefix.

SSRVCMPFCPY, completing copy operation on device _virtual-unit: at LBN: LBN-location, ID number: copy-thread-number
Explanation: The copy operation has completed.
User Action: None.

SSRVCMPMRG, completing merge operation on device _virtual-unit: at LBN: LBN-location, ID number: copy-thread-number
Explanation: The merge operation has completed.
User Action: None.

SSRVCOMPLYFAIL, still out of compliance for per-disk license units, new shadow members may be immediately removed
Explanation: The number of shadow set members on the node has exceeded the number of VOLSHAD-DISK license units for more than 60 minutes. Attempts to bring the node into compliance by removing unlicensed members from their shadow sets have failed. If any new members are mounted, they might be removed immediately.
User Action: Ensure that the number of VOLSHAD-DISK license units on each node is equal to the number of shadow set members mounted on that node. If necessary, dismount shadow set members until the number of mounted members equals the number of VOLSHAD-DISK license units loaded on the node. If you need more VOLSHAD-DISK license PAKs, contact a Digital support representative.

SSRVINICOMP, shadow server has completed initialization
Explanation: The shadow server has been initialized at boot time.
User Action: None.

SSRVINICPY, initiating copy operation on device _virtual-unit: at LBN: LBN-location, I/O Size: number-of-blocks blocks, ID number: copy-thread-number
Explanation: A copy operation is beginning on the shadow set whose virtual unit number is listed in the message.
User Action: None.

SSRVINIMRG, initiating merge operation on device _virtual-unit: at LBN logical-block-number, I/O Size: number-of-blocks blocks, ID number: copy-thread-number
Explanation: A merge operation is beginning on the shadow set. The merge can occur after a copy operation has completed.
User Action: None.

SSRVINIMMRG, initiating minimerge operation on device _virtual-unit: at LBN LBN-location, I/O size: number-of-blocks blocks, ID number: copy-thread-number
Explanation: A shadowing minimerge is beginning on the device indicated. The message identifies the minimerge with the name of the shadow set virtual unit, and the LBN location of the minimerge, the size of the I/O request (in blocks), and the ID number of the copy thread. For example:

%SHADOW_SERVER-I-SSRVINIMMRG, initiating minimerge operation on device _DSA2: at LBN 0, I/O size: 105 blocks, ID number: 33555161

User Action: None.

SSRVINSUFPDL, insufficient per-disk license units loaded, shadow set member(s) will be removed in number minutes
Explanation: The number of shadow set members mounted exceeds the number of VOLSHAD-DISK license units loaded on the node. If this condition is not corrected before the number of minutes displayed in this message has elapsed, Volume Shadowing will remove unlicensed members from shadow sets in an attempt to make the node compliant with the number of loaded VOLSHAD-DISK license units.
User Action: Dismount shadow set members until the number of mounted members is equal to the number of VOLSHAD-DISK license units on the node.

SSRVNORMAL, successful completion of operation on device _virtual-unit: at LBN LBN-location, ID number: copy-thread-number
Explanation: The copy or merge operation has completed.
User Action: None.

SSRVRESCPY, resuming copy operation on device _virtual-unit: at LBN: logical-block-number I/O size: number-of-blocks blocks, ID number: copy-thread-number
Explanation: A copy operation is resuming. The message identifies the copy with a unique sequence number, the name of the shadow set virtual unit, the LBN location of the copy, and the size of the I/O request (in blocks). For example:

%SHADOW_SERVER-I-SSRVRESFCPY, resuming Full-Copy copy sequence number 16777837 on device _DSA101:, at LBN 208314 I/O size: 71 blocks

User Action: None.

SSRVSPNDCPY, suspending operation on device _virtual-unit: at LBN: logical-block-number, ID number: copy-thread-number
Explanation: A copy operation is being interrupted before it completes. (If a crash occurs during a copy operation, a minimerge assist can interrupt the copy operation to resolve inconsistencies. The shadowing software can resume the copy operation when the minimerge completes.) The following message identifies the copy operation with the name of the shadow set virtual unit, the LBN location of the copy, and a unique ID number.

%SHADOW_SERVER-I-SSRVSPNDCPY, suspending operation on device _DSA101:. at LBN: 208314, ID number: 16777837

User Action: None.

SSRVSPNDMMRG, suspending minimerge operation on device _virtual-unit: at LBN: logical-block-number ID number: copy-thread-number
Explanation: A minimerge is interrupted before it completes. The message identifies the minimerge with the name of the shadow set virtual unit, the LBN location of the minimerge, and a unique ID number. For example:

%SHADOW_SERVER-I-SSRVSPNDMMRG, suspending minimerge operation on device _DSA101:. at LBN: 3907911, ID number: 16777837

User Action: None.

SSRVSPNDMRG, suspending merge operation on device _virtual-unit: at LBN: LBN-location, ID number: copy-thread-number
Explanation: A merge operation has been suspended while the shadow set undergoes a copy operation.
User Action: None.

SSRVTRMSTS, reason for termination of operation on device: _virtual-unit:, abort status
Explanation: This message always accompanies the SSRVTERM message to provide further information about the copy termination.
User Action: Possible actions vary depending on the reason for the error. You might need to check and repair hardware or restart the copy operation.

SSRVTERMCPY, terminating operation on device: _virtual-unit:, ID number: copy-thread-number
Explanation: The copy thread is aborting. See the accompanying SSRVTRMSTS message for more information.
User Action: None.

SSRVTERMMRG, terminating operation on device: _virtual-unit:, ID number: copy-thread-number
Explanation: The merge thread is aborting. See the accompanying SSRVTRMSTS message for more information.
User Action: None.

SSRVTERMMMRG, terminating operation on device: _virtual-unit:, ID number: copy-thread-number
Explanation: The minimerge thread is aborting. See the accompanying SSRVTRMSTS message for more information.
User Action: None.

A.4 VOLPROC Messages

Shadowing operations can display the following status messages on the system console (OPA0) and on terminals enabled to receive disk operator messages.

Shadowing messages always include the prefix %SHADOW-I-VOLPROC and can sometimes be followed by "Volume Processing in Progress." The messages are displayed in the following format:

%SHADOW-I-VOLPROC, message-text

• The %SHADOW prefix indicates that the shadowing software is the facility that produced the error.
• I is a one-letter code indicating the status or the severity of the error. The VOLPROC messages are always informational (I) errors.
• VOLPROC is an abbreviation for the volume-processing facility.
• The variable message-text is the description of the status message. For most volume-processing errors, the text includes the virtual unit number or member unit number of the disk or device causing the error.

The following example shows a complete volume-processing status message:

%SHADOW-I-VOLPROC, DSA13: shadow set has changed state. Volume processing in progress.

The following messages are returned by the VOLPROC in response to shadow set operations. The messages in this section are listed in alphabetical order beginning with the first word after the shadow set member name or the virtual unit name. For simplicity, the messages do not include the %SHADOW-I-VOLPROC prefix.

shadow-set-member: contains the wrong volume.
Explanation: The shadowing software discovered a volume label mismatch after failover.
User Action: Check the disk drives and unit numbers.

shadow-set-member: has aborted volume processing.
Explanation: The shadow set is dissolved. A shadow set member was not restored to operational status before the MVTIMEOUT system parameter setting expires; thus, the mount operation aborts for the shadow set.
User Action: Check error logs and the shadow set membership; the disk or controller might need repair.

shadow-set-member: has been write-locked.
Explanation: The data on the disk is protected against write I/O operations.
User Action: Remove the write lock on the volume.

shadow-set-member: has completed volume processing.
Explanation: The shadow set state change is complete.
User Action: Check the shadow set membership; the disk or controller might need repair.

shadow-set-member: is offline.
Explanation: A shadow set member is off line. The shadowing software attempts to fail over.
User Action: None.

shadow-set-member: shadow copy has been completed.
Explanation: A shadow copy operation has completed.
User Action: None.

shadow-set-member: shadow set has been reduced.
Explanation: The specified shadow set member has been removed.
User Action: If the member failed out of the set (not dismounted), look for the cause of the failure and repair it.

virtual-unit: all shadow set copy operations are completed.
Explanation: All pending shadow set copy operations have completed. The same logical block on any shadow set member contains the same data.
User Action: None.

virtual-unit: shadow copy has been started.
Explanation: Indicates the start of a shadow copy operation.
User Action: None.

virtual-unit: shadow master has changed. Dump file will be written if system crashes. Volume Processing in progress.
Explanation: The shadowing software has determined a new master disk for the system disk shadow set. You can write a dump file for this system only if the master is the same disk as the one the system booted from. This is because the boot drivers are not connected with the shadow driver, and different boot drivers from the ones that interact with the booted system disk might be needed to interact with the new master disk. For example, a system disk could be served and also locally connected, causing the served path to use different drivers from the local path.
User Action: None.

virtual-unit: shadow master has changed. Dump file will not be written if the system crashes. Volume processing in progress.
Explanation: Indicates that the disk from which you booted is no longer in the shadow set. If a system failure occurs, a dump file cannot be written to the removed disk.
User Action: Return the disk to the shadow set.

virtual-unit: shadow set has changed state. Volume processing in progress.
Explanation: The state of the shadow set is in transition. The membership of the shadow set is changing because of either the addition or removal of members from the shadow set, or failover to another device after a hardware error. Further messages give details if a change occurs.
User Action: None.

An alphabetical list of terms used in Volume Shadowing for OpenVMS and their definitions follow.

assisted copy: An assisted copy is a copy operation performed within an HSC or HSJ controller in the configuration. The assisted copy does not transfer data through the host node memory. Because the data transfer is from disk to disk, the assisted copy decreases the impact on the system, the I/O bandwidth consumption, and the time required for copy operations. The shadowing software controls the copy operation by using special MSCP copy commands called disk copy data (DCD) commands to instruct the controller to copy specific ranges of logical blocks. For an assisted copy, only one disk can be an active target for a copy at a time.

copy: A copy operation, in the context of Volume Shadowing for OpenVMS, is the process of duplicating the contents of one device onto a second device.

copy fence: A copy fence is a logical boundary between the blocks that have been copied and those that remain to be copied. A copy fence advances with the completion of each copy operation.

DCD: DCD is the acronym for disk copy data, the name of some specialized MSCP commands. The DCD commands are invoked by shadowing software to control assisted copy operations between disks connected to an HSJ controller.

device: Hardware that allows access to storage media; also called drive.

device driver: A software component of the operating system that allows the host computer to communicate with the controller of a device. A device driver exists on the host computer for every peripheral device to which it is attached.

disk: Physical media on which files reside.

dissolve: The act of removing a shadow set from a configuration by removing the virtual unit.

drive: Hardware that allows access to storage media; also called device.

generation number: A generation number is the time stamp assigned to all members of a shadow set by the shadowing software, which the shadowing software uses to track changes in the composition of the shadow set. If a member is removed from a shadow set, the shadowing software updates the generation number of the remaining members.

local write bitmap: A local write bitmap is a bitmap that is created when you mount or dismount a minicopy-enabled shadow set. A local write bitmap communicates with the master write bitmap to ensure that the master write bitmap has a record of all changed blocks. See also write bitmap and master write bitmap.

logical block: Organizational unit of volume space.

logical block number (LBN): A number that identifies a block on a volume. Logical block numbering begins with the first byte in the volume space and continues in a sequentially ascending order through the remainder of the volume space.

master write bitmap: A master write bitmap is created on the first OpenVMS Alpha system that mounts the shadow set. It contains a record of all blocks that have been changed on a shadow set. See also local write bitmap and write bitmap.

merge: A merge operation is an operation to resolve any data inconsistencies between members of a shadow set that could occur when a system fails. A merge operation is declared by the shadowing software for all shadow sets that were mounted on a system that failed.

merge fence: A merge fence is a logical boundary between the blocks that have been compared and those that remain to be compared. A merge fence advances with the completion of each comparison.

minicopy: A minicopy operation is similar to a copy operation, as defined in the context of Volume Shadowing for OpenVMS, except that it copies only the changed blocks. Therefore, the time to perform a minicopy is proportional to the amount of changed blocks on the device. A minicopy operation relies on the existence of a write bitmap for the shadow set.

minimerge: A minimerge operation is similar to a merge operation but faster and requires an HSC or HSJ controller in the configuration. The shadowing software uses a controller-based write log, which shows exactly which blocks had write I/O requests and data security erases (DSEs) outstanding. Only these blocks are made identical.

shadow set: A shadow set consists of up to three devices that are logically bound together by Volume Shadowing for OpenVMS software. The shadow set members are assigned the same virtual unit number, which is stored in the device's storage control block (SCB).

shadow set member: A shadow set member is a device that has been logically bound with other devices into a shadow set.

source device : The device whose contents are copied to a target device.

System Communications Services (SCS): In an OpenVMS Cluster environment, software that implements intercomputer communication, according to the System Communications Architecture (SCA).

target: The device to which the contents of a shadow set member is being copied. When the copy is complete, the target is a member of the shadow set.

virtual unit: A shadow set is represented as a single virtual device, called a virtual unit. A virtual unit is identified by its name DSAn, where n can be any number between 0 and 9999.

volume: Disk or tape media that has been prepared for use by creating a new file structure on it and mounting it on a device.

volume set: A collection of disk volumes bound into a single entity by the DCL command MOUNT/BIND. To users, a volume set looks like a single, large volume.

Also, the volumes on which a set of multivolume files is recorded.

write bitmap: A write bitmap is a data structure in memory that tracks the addresses of all write operations and all data security erase (DSE) operations. See also master write bitmap and local write bitmap.

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