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Procedures CentricStor - Virtual Tape Library
2.6.3 Scratch mount
To prevent reading in from the physical medium in cases where a logical volume is to be
rewritten anyway, under certain circumstances CentricStor performs a “scratch mount”.
The special features of the scratch mount in CentricStor are as follows:
– If the logical volume is migrated, i.e. it is no longer in the TVC, only a “stub” is made
available for the application. This stub contains only the tape headers.
– As this stub is always kept in the TVC a scratch mount can always be performed very
quickly as no restore is required from the physical tape.
– For the application this means that only access to the tape headers is possible.
If a scratch mount is performed incorrectly this can result in read errors when
an attempt is made to access the other data. In this case the data is not lost:
When a subsequent “normal” mount is performed it is available again.
CentricStor performs a scratch mount under the following conditions, depending on the
frontend (interface of the virtual library):
VAMU The mount command supports a flag which can be used to indicate that the
mount is to be performed as a scratch mount.
VDAS There is a special DAS_MOUNT_SCRATCH command (used only by FSC Networ-
ker). In this case CentricStor performs a scratch mount.
VACS A scratch mount is performed in the following two cases:
– “Mount_scratch” with the “pool-ID” parameter without specification of a par-
ticular volume
– Mount on a specific volume if this is contained in a pool whose pool ID is not
0
VLMF A scratch mount is performed in the following two cases:
– Mount with the “scratch” command with specification of a pool or specific vo-
lume
– Mount of a volume that is marked as “scratch”
VJUK No scratch mount is used
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