Hewlett Packard Enterprise HPE XP7, User Manual, Page: 21 / 311

How Fast Snap works
How Fast Snap uses pools and pool volumes
Fast Snap stores snapshot data in THP pools (Pool Type: Thin Provisioning) or Fast Snap pools (Pool
Type: Fast Snap). Unless they are defined otherwise, both THP pools and Fast Snap pools are referred to
as "pools". A pool consists of multiple pool volumes (pool-VOLs) which are, as a group, the container for
the snapshot data.
You must create pools to use Fast Snap. You can create pools and add and delete pool-VOLs from them
using Fast Snap.
The following figure illustrates the relationship between a Fast Snap pair and a pool.
CAUTION: When creating pools, calculate the pool capacity and reserve a sufficient amount of pool
capacity. When you write data to Fast Snap pair volumes and the amount of pool usage exceeds
the pool capacity, the Fast Snap pair is suspended (“PSUE” status), snapshot data is not stored,
and you cannot create additional Fast Snap pairs.
More information
Creating Fast Snap data pools on page 89
Increasing pool capacity on page 155
Decreasing pool capacity on page 159
Deleting pools on page 170
Restoring suspended Fast Snap pairs on page 126
Usage level rebalancing among parity groups
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.
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