Fujitsu Siemens Computers pmn User Manual page 177

GXCC
Further information
Reducing the LV size of an existing LVG:
Increasing the LV size of an existing LVG:
Location
You can use this setting to define the assignment of the cache file system to the LVG.
An LVG can be assigned to precisely one cache file system. However, you can assign
multiple LVGs to a cache file system.
If you select "FLOATING" this means that the LVs of this LVG can be distributed over all
caches to which no LVGs have been explicitly assigned. In addition to "FLOATING" the
names of all the system's caches (e.g. /cache/101) are offered in the selection field.
If you select a specific cache name for an LVG, the LVs of this LVG are moved to or
created in this cache only. This enables you to achieve quasi-residence. Here "quasi-
residence" means that the LVs remain in this cache provided the capacity of the cache
is not exceeded. For example, 250 LVs of 2 GB can be placed in a cache with a size of
500 GB. If you enter a 251st LV in this cache this results in some LV of the other 250
being displaced from the cache. You should always bear this in mind when filling an LVG
which is to contain quasi-resident LVs.
The following should also be taken into consideration in this context: If a logical volume
is mounted, it is always expanded to the maximum size.
Example of an LVG with 2-GB volumes
U41117-J-Z125-7-76
It is not possible to reduce the LV size of an existing LVG in CentricStor.
If you want a smaller LV size, you must create a new LVG with the required LV size.
The data which was written to the large LVs must then be written to the new, smaller
LVs using the customer's (or customer system's) backup tools (host resources).
This is possible provided that the PVs of the LVG offer the required minimum
capacity, otherwise the assignment is rejected with the following message:
The following LVG was(s were) rejected because PV(s) in a linked PVG are
too small to store LVs of the requested LVG-Type size: <LVG_1> <LVG_2>.
If, for example, you have already occuppied 248 GB of the available 250 GB and
now mount 4 logical volumes simultaneously each of which only occupied 1 GB in
the cache beforehand, not 4 GB but 8 GB are now required for these 4 volumes,
which exceeds the maximum size of the cache. Other logical volumes must
therefore be migrated out of this cache, thereby canceling their cache residence.
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