Using INITIALIZE/SHADOW/ERASE to Form a Shadow Set (Integrity servers and Alpha)

On OpenVMS Integrity server systems and OpenVMS Alpha systems, you can use the DCL command INITIALIZE with the /SHADOW and /ERASE command qualifiers to initialize multiple members of a future shadow set. Initializing multiple members in this way eliminates the requirement of a full copy when you later create a shadow set.

The INITIALIZE command with the /SHADOW and /ERASE qualifiers performs the following operations:

Formats up to six devices with one command, so that any three can be subsequently mounted together as members of a new host-based shadow set.
Writes a label on each volume.
Deletes all information from the devices except for the system files and leaves each device with identical file structure information.
All former contents of the disks are lost.

You can then mount up to three of the devices that you have initialized in this way as members of a new host-based shadow set.

Benefits and Side Effects of Using /ERASE

HP strongly recommends that you use the /ERASE qualifier. By using the /ERASE qualifier, a subsequent merge operation is substantially reduced.

If you omit the /ERASE qualifier, then the portions of the volume that do not contain file system data structures contain indeterminate data. This data can differ from one shadow set member to another. Make sure to take this into account when using utilities that compare all of the LBNs between shadow set members. It is important to realize that this is not disk corruption. For more information, see “Using ANALYZE/DISK/SHADOW to Examine a Shadow Set”.

The next time a full merge operation occurs, the presence of this indeterminate data causes the merge to take much longer than it takes without the use of the INITIALIZE/SHADOW/ERASE command. When this full merge completes, the LBNs contain identical data, and the storage control block (SCB) no longer indicates that the /ERASE qualifier was omitted from the INITIALIZE/SHADOW command.

Note, however, that a side effect of using /ERASE is that the ERASE volume attribute is set. In effect, each file on the volume is erased when it is deleted. Another side effect is that an INITIALIZE/ERASE operation is always slower than an INITIALIZE/NOERASE operation. The disks are erased sequentially, which effectively doubles or triples the time it takes for the command to complete. If the disks are large, consider performing multiple, simultaneous INITIALIZE/ERASE commands (with the /SHADOW qualfier) to erase the disks. After all the commands have completed, then perform an INITIALIZE/SHADOW command with the /ERASE qualifier.

You can remove the ERASE volume attribute by issuing the SET VOLUME/NOERASE_ON_DELETE command.

For more information about these DCL commands and qualifiers, see the HP OpenVMS DCL Dictionary.

Requirements for Using INITIALIZE/SHADOW

Starting with OpenVMS Alpha Version 7.3–2, shadow set members can differ in size, that is, they can have different nonzero values for Total Blocks. If devices of different sizes are specified in the INITIALIZE command, and /SIZE or /LIMIT or both are omitted, the default values for these qualifiers take effect. The default value for /SIZE (for the logical volume size for the device) is the smallest member’s MAXBLOCK value. The default value for /LIMIT (for future expansion) is the largest member’s MAXBLOCK value, which is used to compute the expansion limit.

You can view the Total Blocks value by entering the SHOW DEVICE/FULL command. If a device has never been mounted or initialized on this system, the SHOW DEVICE/FULL command for the device does not display a value for Total Blocks. To correct this condition, either mount and then dismount the device, or initialize the device. The Total Blocks value is then displayed by SHOW DEVICE/FULL.

The use of INITIALIZE/SHADOW requires the VOLPRO privilege.

Note that the INITIALIZE/SHADOW command must not be used to initialize a disk to be added to an existing shadow set, since there is no benefit to be gained.

The format of this command follows:

INITIALIZE/SHADOW=(device_name1, device_name2, device_name3) label

INITIALIZE/SHADOW Examples

The following example shows the correct use of this command. Note that the command specifies multiple devices on the same line.

$ INITIALIZE /ERASE /SHADOW=($4$DKA1300, $4$DKA1301) NONVOLATILE
$ MOUNT/SYS DSA42 /SHAD=( $4$DKA1300 , $4$DKA1301 ) NONVOLATILE
%MOUNT-I-MOUNTED, NONVOLATILE MOUNTED ON _DSA42:
%MOUNT-I-SHDWMEMSUCC, _$4$DKA1300: (WILD3) IS NOW A VALID MEMBER OF THE SHADOW SET 
%MOUNT-I-SHDWMEMSUCC, _$4$DKA1301: (WILD4) IS NOW A VALID MEMBER OF THE SHADOW SET
$ SHO DEV DSA42:

DEVICE               DEVICE           ERROR    VOLUME         FREE  TRANS MNT
 NAME                STATUS           COUNT     LABEL        BLOCKS COUNT CNT
DSA42:               MOUNTED              0  NONVOLATILE    5799600     1   1
$4$DKA1300: (WILD3)  SHADOWSETMEMBER      0  (MEMBER OF DSA42:)
$4$DKA1301: (WILD4)  SHADOWSETMEMBER      0  (MEMBER OF DSA42:)

The following example shows an incorrect use of this command. Do not use a separate command to initialize each device.

$ INITIALIZE /ERASE /SHADOW=  $4$DKA1300 NONVOLATILE                       
$ INITIALIZE /ERASE /SHADOW=  $4$DKA1301 NONVOLATILE

$ MOUNT/SYS DSA42 /SHAD=( $4$DKA1300 , $4$DKA1301 ) NONVOLATILE
%MOUNT-I-MOUNTED, NONVOLATILE MOUNTED ON _DSA42:
%MOUNT-I-SHDWMEMSUCC, _$4$DKA1300: (WILD3) IS NOW A VALID MEMBER OF THE SHADOW SET 
%MOUNT-I-SHDWMEMSUCC, _$4$DKA1301: (WILD4) IS NOW A VALID MEMBER OF THE SHADOW SET
$ SHO DEV DSA42:

DEVICE               DEVICE           ERROR    VOLUME         FREE  TRANS MNT
 NAME                STATUS           COUNT     LABEL        BLOCKS COUNT CNT
DSA42:               MOUNTED              0  NONVOLATILE    5799600     1   1
$4$DKA1300:    (WILD3)  ShadowSetMember      0  (member of DSA42:)
$4$DKA1301:    (WILD4)  ShadowCopying        0  (copy trgt DSA42:   0% copied)