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CentricStor - Virtual Tape Library Administering the tape cartridges
2.5.4 Reorganization of the tape cartridges
When a logical volume is released by the host’s volume management facility (e.g. MAREN
in BS2000/OSD), it is flagged accordingly in the CentricStor data maintenance facility which
contains the metadata for each volume. This process, combined with updates (see the
section section “Creating a directory” on page 36), will cause the areas containing invalid
data on the real tape cartridges to increase more and more over time (stacked volume with
gaps). If the number of scratch tapes for a CentricStor system falls below a configurable
lower limit, the PLM automatically performs a reorganization by using the VLM to load any
logical volumes still valid into the RAID system and then, so to speak, moving them
piecemeal onto scratch tapes.
Figure 12: Example of a reorganization
Read tape: Tape cartridge that still contains valid data but has no free space for write
operations
Scratch tape: Tape cartridge that only contains invalid data and has been released for
rewriting
Write tape: Tape cartridge that still contains space for write operations
LV0000 LV0001
LV0002
LV0003
LV0004
LV0005
LV0006 LV0007 LV0008
LV0011LV0009
LV0010
PV0000
PV0001
PV0002
PV0000
PV0001
PV0002
VLM
CentricStor
:
:
LV0037
PV0007
PV0008
:
:
LV0037
PV0007
PV0008
LV0000 LV0001
LV0002
LV0003
LV0004
LV0005
LV0006 LV0007 LV0008
LV0011LV0009
LV0010
LV0001
LV0002
LV0003
LV0006 LV0007
LV0011LV0009
Scratch tapes
:
:
:
:
Write tapes
PLM
TVC
Read tapes