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Rebalancing is performed as if each parity group were a single pool-VOL.
After rebalancing, the usage rates of LDEVs in a parity group may not be
balanced, but the usage rate in the entire pool is balanced.
The usage level among parity groups is automatically rebalanced when
expanding or shrinking pool capacity operations are in progress.
If you expand the pool capacity, Dynamic Provisioning moves data to the
added space on a per-page basis. When the data is moved, the usage rate
among parity groups of the pool-VOLs is rebalanced.
Host I/O performance may decrease when data is moved. If you do not want
to have the usage level of parity groups automatically balanced, call
customer support.
You can see the rebalancing progress of the usage level among parity groups
in the
View Pool Management Status
window. Dynamic Provisioning
automatically stops balancing the usage levels among parity groups if the
cache memory is not redundant or the pool usage rate reaches up to the
threshold.
Related tasks
•
Viewing formatted pool capacity and pool usage rates
on page 173
How Thin Image uses V-VOLs
V-VOLs are virtual volumes that do not have any physical storage space.
Thin Image uses V-VOLs (V-VOLs of provisioning type Snapshot) or DP-VOL
as V-VOLs. Thin Image V-VOLs and DP-VOLs are referred to as virtual
volumes (V-VOLs) in this document. Use DP-VOLs to create cascaded or
cloned pairs. Use Thin Image V-VOLs to create snapshot pairs. Note that you
can use DP-VOLs to cascade snapshot pairs.
Thin Image uses V-VOLs to access snapshot data from hosts or clone pairs,
so if you create clone pairs or use snapshot pairs (a pair with the snapshot
attribute) to access snapshot data from hosts, then V-VOLs are required to
create Thin Image pairs or assign an S-VOL to snapshot data. If the storage
system or snapshot pair does not need to access snapshot data from hosts,
V-VOLs are not necessary.
You can release the V-VOLs that are being used as Thin Image S-VOLs from
assignment of snapshot data. Released V-VOLs can be assigned to other
snapshot data. However, you cannot release allocation of V-VOLs used as
node volumes to snapshot data or allocate the V-VOL to different snapshot
data. Also, you cannot release allocation of V-VOLs which are being used for
the S-VOL of a clone pair to snapshot data, or allocate it to different snapshot
data.
28
Overview of Thin Image
Hitachi Thin Image User Guide for Hitachi Virtual Storage Platform G Series and F Series