Document revision date: 30 March 2001

## Volume Shadowing for OpenVMS

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## 4.8 Removing Members and Dissolving Shadow Sets

You can remove shadow set members and dissolve shadow sets with the DCL command DISMOUNT. You must have GRPNAM and SYSNAM user privileges to dismount group and system volumes. The DISMOUNT command has the following format:

`DISMOUNT {device-name[:] virtual-unit-name}`

The action taken differs depending on whether you specify an individual shadow set member or the shadow set (by its virtual unit name) on the DISMOUNT command:

- If you specify the device name of a shadow set member, only that member is dismounted, and the remaining shadow set members continue servicing I/O requests.
- If you specify a shadow set virtual unit, all shadow set members are dismounted and the shadow set is dissolved.

To dismount a shadow set that is mounted across an OpenVMS Cluster system, include the /CLUSTER qualifier with the DISMOUNT command. If you dismount a shadow set without including the /CLUSTER qualifier, only the node from which you issued the command dismounts the shadow set. The shadow set remains operational on the other OpenVMS Cluster nodes that have the shadow set mounted.

If the disks on your system are neither SCSI nor Fibre Channel disks, you can use the /NOUNLOAD qualifier on the DISMOUNT command to prevent the disk volume or volumes from spinning down. The devices remain in a ready state. If you specify the /UNLOAD qualifier when dismounting a virtual unit, the disk volumes are physically spun down after the shadow set is dissolved. See the OpenVMS DCL Dictionary for more information about using the DISMOUNT command and its qualifiers.

### 4.8.1 Removing Members from Shadow Sets

To remove an individual member from a shadow set, specify the name of the physical device with the DISMOUNT command. For example:

    $ DISMOUNT $5$DUA7:

When you dismount an individual shadow set member, all outstanding I/O operations are completed and the member is removed from the set.

Starting with OpenVMS Alpha Version 7.3, the /FORCE_REMOVAL ddcu: qualifier is available. If connectivity to a device has been lost and the shadow set is in mount verification, `/FORCE_REMOVAL ddcu:` can be used to immediately expel a named shadow set member (ddcu:) from the shadow set. If you omit this qualifier, the device is not dismounted until mount verification completes. Note that this qualifier cannot be used in conjunction with the /POLICY=MINICOPY (=OPTIONAL) qualifier.

The device specified must be a member of a shadow set that is mounted on the node where the command is issued.

This qualifier gives system managers greater control of shadow sets whose members are located at different sites in an OpenVMS Cluster configuration. SET DEVICE command qualifiers are also available for specifying disaster-tolerant management attributes for shadow set members, as described in Section 4.7.

Note You cannot dismount a device if it is the only source member in a shadow set. All shadow sets must have at least one valid source member. If you try to dismount the only source member device, the DISMOUNT command fails and returns the message:
    %DISM-F-SRCMEM, Only source member of shadow set cannot be dismounted
The only way to dismount the last source member of a shadow set is to dissolve the shadow set by specifying the virtual unit name on the DISMOUNT command.

### 4.8.2 Dissolving Shadow Sets

You dissolve a shadow set by specifying its virtual unit name with the DISMOUNT command. Specifying the virtual unit name causes all members in the shadow set to be dismounted, thereby dissolving the shadow set on the node that issues the DISMOUNT command. The command in Example 4-9 includes the /CLUSTER qualifier to dissolve the DSA36 shadow set across an OpenVMS Cluster system.

Example 4-9 Dissolving a Shadow Set

    $ DISMOUNT /CLUSTER DSA36:

Dismounting the virtual unit can be done only after all files are closed, thereby ensuring that the dismounted disks are fully consistent from a file system perspective. The dismount operation marks the shadow set members as being properly dismounted so that a rebuild is not required the next time the disks are mounted. However, if a merge operation was either pending or in progress, then the dismount operation marks the shadow set members as being improperly dismounted and requires a merge operation.

Note If you dismount a virtual unit while a copy operation is in progress for the shadow set, the copy operation aborts and the shadow set is dissolved. You receive OPCOM messages similar to those in the following example:
    $ DISMOUNT DSA9999:
    %%%%%%%%%%%  OPCOM  24-MAR-1990 20:29:57.52  %%%%%%%%%%%
    $7$DUA6:  (WRKDSK) has been removed from shadow set.
    %%%%%%%%%%%  OPCOM  24-MAR-1990 20:29:57.68  %%%%%%%%%%%
    $7$DUA56: (PLADSK)  has been removed from shadow set.
    %%%%%%%%%%%  OPCOM  24-MAR-1990 20:29:57.88  %%%%%%%%%%%
    Message from user SYSTEM on SYSTMX

### 4.8.3 Dismounting and Remounting With One Less Member for Backup

As discussed in Section 4.8.2, the virtual unit can be dismounted on the system or across an OpenVMS Cluster system. To ensure that the virtual unit has been dismounted correctly, the following steps are recommended:

1. Issue the MOUNT/NOWRITE command, followed by the SHOW DEVICE command, for example:

       $ MOUNT/NOWRITE DSA42: /SHADOW=($4$DUA3,$4$DUA4,$4$DUA5) volume-label
       $ SHOW DEVICE DSA42:

2. Observe that the virtual unit is in a steady state; that is, all members are consistent and no copy or merge operation is in progress. If a copy or merge operation is in progress, you must wait for the operation to complete.
3. When the virtual unit is in a steady state, remove a member from the shadow set with the DISMOUNT command, as shown in the following example:

       $ DISMOUNT $4$DUA5

4. Dismount the virtual unit and then remount it with one less member, as shown by the following command:

       $ MOUNT/SYS DSA42: /SHADOW=($4$DUA3,$4$DUA4) volume-label

   The shadow set member that was removed can now be used for a backup operation of the virtual unit.

Note If your application must run continuously (that is, you cannot dismount the virtual unit without disrupting your business), you can still remove a shadow set member that you plan to return later to the shadow set. Your application and recovery procedures must be designed to ensure data consistency, as described in Section 7.12.

## 4.9 Displaying Information About Shadow Sets

You can use the DCL command SHOW DEVICE or the F$GETDVI lexical function to get information about a shadow set virtual unit and the physical volumes that make up the members. You can also use the System Dump Analyzer (SDA) to get more information about shadow sets.

The following sections describe how to use these tools to examine volume shadowing virtual units and shadow set members. See also the OpenVMS DCL Dictionary for a full description of how to use the SHOW DEVICE command and the F$GETDVI lexical function. See the OpenVMS Alpha System Analysis Tools Manual and the OpenVMS VAX System Dump Analyzer Utility Manual for more information about how to use SDA on OpenVMS Alpha and OpenVMS VAX systems, respectively.

You can use any of the SHOW DEVICE qualifiers when you examine shadow sets (by specifying a shadow set's virtual unit name) or shadow set members.

Note Because shadow sets are created and maintained individually on each node in the OpenVMS Cluster, the SHOW DEVICE display does not list shadow sets that have been created on only remote nodes.

### 4.9.1 Listing Shadow Sets

Use SHOW DEVICE in the following format to display information about shadow sets:

`SHOW DEVICE [virtual-unit-name[:]]`

The variable virtual-unit-name replaces device-name as the SHOW DEVICE command parameter for shadow sets. Use the virtual unit naming format DSAn:.

As with any SHOW DEVICE command, the colon is optional. Note also that you can specify a complete virtual unit name (or a portion of a virtual unit name) just as you can with device names. If you omit the virtual unit number, SHOW DEVICE lists all the shadow set virtual units that represent shadow set member disks of the type specified. If you truncate a device name (for example, if you specify D), SHOW DEVICE lists all the devices and all the virtual units that begin with the letters you entered (in this case, D).

When you specify the virtual unit number, SHOW DEVICE displays the names of the shadow set members it represents. If you use the /FULL qualifier, SHOW DEVICE displays full information about the shadow set and all the associated shadow set members.

Because individual shadow set members that are mounted for systemwide or clusterwide access are not allocated or mounted in the traditional sense, a SHOW DEVICE command with the /ALLOCATED or /MOUNTED qualifiers displays only virtual units.

### 4.9.2 Listing Shadow Set Members

Use the same format for the SHOW DEVICE command with shadow set members as you use with other physical devices. The command lists all shadow set members of the device name you specify.

Because shadow set members are not mounted in a traditional sense and they all have the same device characteristics, SHOW DEVICE displays most of the relevant data with the associated virtual unit. Listings of shadow set members include information about current membership status.

If a shadow set is undergoing a copy or a merge operation, the display resulting from the SHOW DEVICE command includes the percentage of the disk that has been copied or merged. The SHOW DEVICE information is available on all nodes that have the shadow set mounted.

The SHOW DEVICE display indicates the exact percentage of the disk that has been copied. The node that is managing the copy operation knows precisely how far the copy or merge operation has progressed, and periodically notifies the other nodes in the OpenVMS Cluster of the progress. Thus, the other nodes in the cluster know approximately the percentage copied. When you enter the SHOW DEVICE command from a node other than the one where the copy or merge operation is taking place, the number indicating the percentage copied in the SHOW DEVICE output lags (by a small percentage) the actual percentage copied.

Note that if a copy and a merge operation are occurring at the same time in the same shadow set, the number indicating the percentage merged remains static until the copy completes. Then the merge operation proceeds to completion.

### 4.9.3 SHOW DEVICE Examples for Shadow Set Information

The following examples of output from the SHOW DEVICE command illustrate the types of shadow set information you can obtain, such as shadow set membership and the status of each shadow set member during copy and merge operations. For examples of output for write bitmaps used with the minicopy operation, see Section 7.10.

###

#### Examples

#1
    $ SHOW DEVICE D
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA0:                Mounted           0  SHADOWDISK        8694   151   1
    DSA9999:             Mounted           0  APPARITION      292971     1   1
    $4$DUA0:   (SYSTMX)  Online            0
    $4$DUA8:   (HSJ001)  ShadowSetMember   0  (member of DSA0:)
    $4$DUA10:  (SYSTMX)  ShadowSetMember   0  (member of DSA9999:)
    $4$DUA11:  (SYSTMX)  ShadowSetMember   0  (member of DSA9999:)
    $4$DUA12:  (SYSTMX)  ShadowSetMember   0  (member of DSA9999:)
    $4$DUA89:  (HSJ002)  ShadowSetMember   0  (member of DSA0:)

> By truncating the device name, you cause the SHOW DEVICE command to list all the devices and all the virtual units on the local node that begin with the letters you entered (in this case, D). This example shows that two virtual units, DSA0 and DSA9999, are active. Both shadow sets are in a steady state. The device status "ShadowSetMember" indicates that the shadow set is in a steady state---the shadow set members are consistent with each other.

#2
    $ SHOW DEVICE DSA8
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA8:                Mounted           0  APPARITION      890937     1   1
    $11$DUA8:   (SYSTMX)   ShadowSetMember   0  (member of DSA8:)
    $11$DUA89:  (SYSTMY)   ShadowSetMember   0  (member of DSA8:)

> This example shows the membership and status of the shadow set represented by the DSA8 virtual unit. The SHOW DEVICE display provides information not only about the virtual unit DSA8, but also about the physical devices $11$DUA8 and $11$DUA89 that are members of the shadow set. The device status "ShadowSetMember" indicates that the shadow set is in a steady state---the shadow set members are consistent with each other. The shadow set members are being served by OpenVMS Cluster nodes SYSTMX and SYSTMY.

#3
    $ SHOW DEVICE DSA
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA7:                Mounted           0  PHANTOM          27060    35   7
    DSA8:                Mounted           0  APPARITION      890937     4   6

> You might specify DSA on the SHOW DEVICE command to request information about all the shadow sets on the local node. Entering a generic virtual unit name, such as DSA, as a parameter produces a display of all virtual units representing shadow sets mounted on the local system. This example shows that two shadow sets are mounted on the local node, represented by the virtual units DSA7 and DSA8.

#4
    $ SHOW DEVICE $11$DUA8:
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA8:                Mounted           0  APPARITION      890937     1   1
    $11$DUA8:   (HSJ001) ShadowSetMember   0  (member of DSA8:)
    $11$DUA89:  (HSJ002) ShadowSetMember   0  (member of DSA8:)

> Although the SHOW DEVICE command specifies the name of a single device, the resulting display includes information about the membership and status of the shadow set represented by the DSA8 virtual unit to which the $11$DUA8 device belongs. The device status "ShadowSetMember" indicates that the shadow set is in a steady state---the shadow set members are consistent with each other. The shadow set members are accessed through the node named HSJ001.

#5
    $ SHOW DEVICE $11$DUA8:
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA8:                Mounted           0  APPARITION      890937     1   1
    $11$DUA8:  (HSJ001)  ShadowSetMember   0  (member of DSA8:)

    $11$DUA89: (HSJ002)  ShadowCopying     0  (copy trgt DSA8:  48% copied)

> The output from this SHOW DEVICE command shows a shadow set that is in a transient state. The device status "ShadowCopying" indicates that the physical device $11$DUA89 is the target of a copy operation, and 48% of the disk has been copied. The device $11$DUA8 is the source member for the copy operation.

#6
    $ SHOW DEVICE DSA8
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA8:                Mounted           0  APPARITION      890937     1  12

    $11$DUA8:  (HSJ001)  ShadowCopying     0  (copy trgt DSA8: 5% copied)
    $11$DUA89: (HSJ002)  ShadowMergeMbr    0  (merging DSA8:   0% merged)

> This example shows how the SHOW DEVICE command displays a shadow set during a copy operation after a node in an OpenVMS Cluster system fails. In this example, the shadow set members are located on different nodes in the cluster, and one node on which the shadow set is mounted fails. At the time of the failure, the shadow set was in a transient state, with the $11$DUA8 device undergoing a copy operation. The SHOW DEVICE command shows the state of the shadow set during the copy operation, before the merge operation occurs.

> At the same time the $11$DUA89 shadow set member is acting as the source member for the copy operation, $11$DUA89 also accepts and performs I/O requests from applications running on the OpenVMS Cluster system. Once the copy operation completes, a merge operation automatically starts. See Chapter 6 for more information about merge operations.

> The next example shows how the SHOW DEVICE command display looks during the merge operation.

#7
    $ SHOW DEVICE DSA8
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA8:                Mounted           0  APPARITION      890937     1   1

    $11$DUA8:   (HSJ001) ShadowMergeMbr    0  (merging DSA8: 78% merged)
    $11$DUA89:  (HSJ002) ShadowMergeMbr    0  (merging DSA8: 78% merged)

> The SHOW DEVICE command produces a display similar to this example when a shadow set is in a transient state because of a merge operation. The merge operation is 78% complete.

#8
    $ SHOW DEV D
    Device               Device        Error    Volume         Free  Trans Mnt
     Name                Status        Count     Label        Blocks Count Cnt
    DSA456:      (FUSS)  Mounted           0  AUDITINGDISK    123189   225  17
    $11$DIA1:  (LISBEN)  Online            0
    $11$DJA16: (GALEXI)  Online            0
    $11$DJA128:(GALEXI)  Mounted wrtlck    0  CORPORATEVOL    164367     1  18
    $11$DJA134:(GALEXI)  Mounted           0  WORKVOLUME      250344     1  16
    $11$DUA1:    (FUSS)  Mounted           0  MAR24DISKVOL    676890     1  18
    $11$DUA2:    (FUSS)  ShadowSetMember   0  (member of DSA456:)
    $11$DUA7:   (BLISS)  Online            0  (remote shadow member)
    $11$DUA11: (LISBEN)  Mounted           0  RMSFILES        621183     1  18
    $11$DUA13:  (BLISS)  Mounted           0  RESIDENTVOL     525375     1  18

> This example shows how the SHOW DEVICE command displays remote shadow set members. In this display, the device $11$DUA7, whose description is "remote shadow member," is a member of a shadow set that is not mounted on this system.

#9
    $ SHOW DEVICE/FULL DSA80
    Disk DSA80:, device type MSCP served SCSI disk, is online, mounted, file-
    oriented device, shareable, available to cluster, error logging is enabled.

    Error count                    0    Operations completed               138
    Owner process                 ""    Owner UIC                      [SHADOW]
    Owner process ID        00000000    Dev Prot    S:RWED,O:RWED,G:RWED,W:RWED
    Reference count                1    Default buffer size                512
    Total blocks              891072    Sectors per track                   51
    Total cylinders             1248    Tracks per cylinder                 14
    Volume label         "SHADTEST1"    Relative volume number               0
    Cluster size                   3    Transaction count                    1
    Free blocks               890937    Maximum files allowed           111384
    Extend quantity                5    Mount count                          4
    Mount status              System    Cache name         "_DSA2010:XQPCACHE"
    Extent cache size             64    Maximum blocks in extent cache   89093
    File ID cache size            64    Blocks currently in extent cache     0
    Quota cache size               0    Maximum buffers in FCP cache       216
    Volume status:  subject to mount verification, file high-water marking,write-
      through caching enabled.
    Volume is also mounted on BLASTA, CNASTA, SHASTA.
    Disk $255$DUA56:, device type MSCP served SCSI disk, is online, member of
    shadow set DSA80:, error logging is enabled.
    Error count                    0    Shadow member operation count      301
    Host name               "SHASTA"    Host type, avail      VAX 6000-320,yes
    Allocation class             255
      Volume status:  volume is a merge member of the shadow set.
    Disk $255$DUA58:, device type MSCP served SCSI disk, is online, member of
    shadow set DSA80:, error logging is enabled.
    Error count                    0    Shadow member operation count      107
    Host name               "SHASTA"    Host type, avail      VAX 6000-320,yes
    Allocation class             255
    Volume status:  volume is a merge member of the shadow set.

> This example shows how the SHOW DEVICE/FULL command displays detailed information about the shadow set and its members. Notice that both members, $255$DUA56 and $255$DUA58, are merge members. Section 4.9.4 shows what this shadow set looks like when it is examined using the System Dump Analyzer.

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