skip book previous and next navigation links
go up to top of book: HP Volume Shadowing for OpenVMS HP Volume Shadowing for OpenVMS
go to beginning of chapter: Creating and Managing Shadow Sets Using DCL Commands Creating and Managing Shadow Sets Using DCL Commands
go to previous page: Creating a Shadow Set Creating a Shadow Set
go to next page: MOUNT Command Qualifiers for ShadowingMOUNT Command Qualifiers for Shadowing
end of book navigation links

Using INITIALIZE/SHADOW/ERASE to Streamline the Formation of a Shadow Set  



On 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:

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 will be substantially reduced.

If you omit the /ERASE qualifier, then the portions of the volume that do not contain file system data structures will 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.

The next time a full merge operation occurs, the presence of this indeterminate data will cause the merge to take much longer than it would have without use of the INITIALIZE/SHADOW/ERASE command. When this full merge completes, the LBNs will contain identical data, and the storage control block (SCB) will no longer indicate 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 command 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 will be 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 should 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)

go to previous page: Creating a Shadow Set Creating a Shadow Set
go to next page: MOUNT Command Qualifiers for ShadowingMOUNT Command Qualifiers for Shadowing