Copy Operation: Creating a New Shadow Set shows whathappens when you create a shadow set by mounting two disk volumesthat have never been a part of a shadow set. Because neither diskvolume has been a part of a shadow set, the Mount utility (MOUNT)assumes that the first disk named in the MOUNT command is the sourcemember. When the Mount utility checks the volume labels on the disks,it discovers that they are different from each other, and the utilityautomatically performs a copy operation.
In this example, DSA0 is the virtual unit name, $1$DUA8 and$1$DUA89 are the names of the disk volumes, and SHADOWDISK is thevolume label.
Example 1 Copy Operation: Creating a New Shadow Set
$ MOUNT DSA0: /SHADOW=($1$DUA8:,$1$DUA89:) SHADOWDISK %MOUNT-I-MOUNTED, SHADOWDISK mounted on _DSA0: %MOUNT-I-SHDWMEMSUCC, _$1$DUA8: (FUSS) is now a valid member of the shadow set %MOUNT-I-SHDWMEMCOPY, _$1$DUA89: (FUSS) added to the shadow set with a copy operation $ SHOW DEVICE DSA0: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA0: Mounted 0 SHADOWDISK 890937 1 1 $1$DUA8: (FUSS) ShadowSetMember 0 (member of DSA0:)
The SHOW DEVICE display in Copy Operation: Creating a New Shadow Set shows the shadow set during the copy operation(transient state). Because the SCB information on $1$DUA8 and $1$DUA89indicates that these devices have never been part of a shadow set,the shadowing software uses the first device named in the commandline ($1$DUA8) as the source of the copy operation. The device status "ShadowSetMember" indicatesthat the $1$DUA8 device is a source shadow set member, and "ShadowCopying" indicatesthat the physical device $11$DUA89 is the target of a copy operation.
Suppose you want to add a new member to an existing shadowset, and the device you add is a previous member of this same shadowset. In this case, the volume label of the new member matches thatof the current shadow set members, but the new member's MOUNT generationnumber is out of date compared with those of the current members.Thus, the Mount utility automatically performs a copy operationon that member.
Copy Operation: Adding a Member to an Existing Shadow Set shows theformat of the MOUNT command and MOUNT status messages returned whenyou add the $3$DIA12 device to the shadow set represented by theDSA9999 virtual unit. Notice that you do not need to list the memberunits currently in the shadow set on the MOUNT command line.
Example 2 Copy Operation: Adding a Member to an ExistingShadow Set
$ MOUNT /SYSTEM DSA9999: /SHADOW=$3$DIA12: AXP_SYS_071 %MOUNT-I-MOUNTED, AXP_SYS_071 mounted on _DSA9999: %MOUNT-I-SHDWMEMCOPY, _$3$DIA12: (SHAD03) added to the shadow set with a copy operation $ SHOW DEVICE DSA9999: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA9999: Mounted 0 AXP_SYS_071 70610 1 1 $3$DIA7: (BGFUSS) ShadowSetMember 0 (member of DSA9999:) $3$DIA5: (SHAD03) ShadowSetMember 0 (member of DSA9999:)
No Copy Operation: Rebuilding a Shadow Set shows whathappens when a three-member shadow set is dissolved on one nodeand then is immediately remounted on another node. When the Mountutility checks the volume information on each member, it finds thatthe volume information is consistent across the shadow set. Thus,a copy operation is not necessary when the shadow set is mounted.
In No Copy Operation: Rebuilding a Shadow Set, DSA10 isthe virtual unit and $3$DUA10, $3$DUA11, and $3$DUA12 are the member volumes.The first part of the example displays the output from a SHOW DEVICEcommand, which shows that the shadow set is mounted and in a steadystate. Then the user dismounts the DSA10 shadow set and immediatelyremounts it.
Example 3 No Copy Operation: Rebuilding a Shadow Set
$ SHOW DEVICE D Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA10: Mounted 0 VAX_SYS_071 292971 1 1 $3$DUA10: (MYNODE) ShadowSetMember 0 (member of DSA10:) $3$DUA11: (MYNODE) ShadowSetMember 0 (member of DSA10:) $3$DUA12: (MYNODE) ShadowSetMember 0 (member of DSA10:) $ DISMOUNT /NOUNLOAD DSA10: %%%%%%%%%%% OPCOM 24-MAR-1997 20:26:41.40 %%%%%%%%%%% $3$DUA10: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1997 20:26:41.69 %%%%%%%%%%% $3$DUA11: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1997 20:26:41.69 %%%%%%%%%%% $3$DUA12: (MYNODE) has been removed from shadow set. %%%%%%%%%%% OPCOM 24-MAR-1997 20:26:41.69 %%%%%%%%%%% $ MOUNT /SYSTEM DSA10: /SHADOW=($3$DUA10:, $3$DUA11:, $3$DUA12:) VAX_SYS_071 %MOUNT-I-MOUNTED, VAX_SYS_071 mounted on _DSA10: %MOUNT-I-SHDWMEMSUCC, _$3$DUA10: (MYNODE) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$3$DUA11: (MYNODE) is now a valid member of the shadow set %MOUNT-I-SHDWMEMSUCC, _$3$DUA12: (MYNODE) is now a valid member of the shadow set $
When a system fails, the volume information is left in a statethat shows that each shadow set member was not properly dismounted.If you issue the MOUNT command again after the node reboots, theshadowing software automatically performs a merge operation on theshadow set.
Example 4 Merge Operation: Rebuilding a Shadow Set
$ SHOW DEVICE DSA42: Device Device Error Volume Free Trans Mnt Name Status Count Label Blocks Count Cnt DSA42: Mounted 0 ATHRUZ 565997 1 1
HP Volume Shadowing for OpenVMS
Ensuring Shadow Set Consistency
