When the VTPOOL member is being used to define the Virtual VOLSER range or ranges, newly scratched Virtual VOLSERs are immediately returned to the Scratch Pool and assigned a reuse date. CA Vtape will not reuse these VOLSERs until five days have passed or no other scratch VOLSERs are available. If enough of an appropriate number of VOLSERs are defined, this provides a five day recovery window before an accidentally scratched Virtual VOLSER is reused.
If the defined VOLSER ranges are broken up into separate subpools, a Scratch Pool is maintained for each subpool. Newly scratched Virtual VOLSERS are returned to the appropriate Scratch Pool and assigned a reuse date.
Each Scratch Pool is broken up into extents that are activated and deactivated individually. An extent consists of a set of 100 consecutive VOLSERs from xxxx00-xxxx99. When all scratch VOLSERs with a scratch date older than five days are depleted in an extent, the extent is deactivated and the next extent is activated. If all scratch VOLSERs older than five days are depleted in all extents, a second pass is made for the first available scratch VOLSER. The deactivation and activation of extents causes the Virtual VOLSERs to be chosen in order from lowest to highest in a round-robin fashion.
In the following example, V00006 is currently the next available scratch VOLSER in the currently active extent 3. If the Scratch Synchronization Job runs and makes V00001, V00002, and V00004 available for reuse, the active extent and the next available scratch pointer will not be changed. V00006 will still be the next available VOLSER. The next scratch mount request will use V00006 and turn it off. V00007 will then be the next available VOLSER. When V00007 is used, extent 3 will be deactivated and extent 1 will be activated.
BEFORE SYNCH AFTER SYNCH AFTER NEXT MOUNT V00000 V00000 V00000 Extent 1* V00001 V00001 On V00001 On V00002 V00002 On V00002 On V00003 V00003 V00003 Extent 2* V00004 V00004 On V00004 On V00005 V00005 V00005 V00006 On <- V00006 On <- V00006 Extent 3* <- V00007 On V00007 On V00007 On <- V00008 V00008 V00008 * The extents were artificially shortened to three VOLSERs.
Note: When Virtual Volume Pooling is active, the SVTn ADD VVP and DELETE VVP console commands are deactivated. Changes to the Virtual VOLSER ranges are performed by updating the VTPOOL member and issuing the SVTn REFRESH=POOLS console command.
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