Hp XP P9500 Storage User Manual download pdf (Page 33)

Effects on I/O performance of the storage system

If you perform FS restore tasks when the workload on the storage system is high, I/O performance

of host servers can decline because replication process starts for the P-VOL. Enable the copy

threshold option to lower the workload on the storage system..

For more information, see “Copy threshold option” (page 16).

For more information about enabling the copy threshold option, contact HP Technical Support.

Calculating pool capacity

Calculate the capacity of which snapshot data you can store in the pool by subtracting the capacity

of V-VOL management areas from the total capacity of pool-VOLs in the pool. The capacity of

V-VOL management areas is 3% of the pool capacity. If the pool capacity is insufficient, the status

of FS pairs can change to “PSUE”. In this case, estimate the capacity of snapshot data to be copied

to the pool and assign the pool capacity based on the estimate. If the capacity of snapshot data

to be copied to the pool varies hour by hour, ensure that the largest capacity is your pool capacity.

• If snapshot data is copied to the pool, the pool capacity is always consumed in units of 42

megabytes. Even if snapshot data is smaller than 42 megabytes, at least 42 megabytes of

pool capacity is needed.

• If you write data to the same area in the P-VOL more than one time, snapshot data is copied

to the pool only when data is written for the first time. If data is written to the same area only

once, the capacity of written data equals to the capacity of snapshot data to be copied to the

pool. If data is written to the same area more than once, the capacity of snapshot data to be

copied to the pool is smaller than the capacity of written data.

• Specify the capacity of a pool-VOL in multiples of 42 megabytes to avoid truncation.

Pool capacity calculations

To decide the capacity of pools, estimate the capacity of snapshot data that you want to copy.

The capacity of snapshot data that you want to copy equals to the capacity of data written to the

same area in the P-VOL during the period from when you stored the snapshot data to when you

deleted the snapshot data.

If you have stored multiple snapshot data, you can share the data in a pool. If the snapshot data

contains the shared data, you can release FS pairs, but you cannot delete the snapshot data from

the pool. If you release the FS pairs that have snapshot data containing the shared data, the

snapshot data are also deleted from the pool.

Complete the following to create a backup of data using FS:

1. Store the snapshot data.

2. Use an S-VOL.

NOTE: During this process, a significant amount of data is read from the S-VOL. This can increase

the accesses to the P-VOL and degrade the host I/O performance.

The target for the backup is only the areas where the snapshot data is stored. Therefore, you can

create a backup copy even if the pool capacity is small.

Although pool capacity is decided according to the estimation, if the pool capacity exceeds the

threshold, address the issue.

For more information about addressing threshold issues, see “General troubleshooting” (page 64).

Using external volumes as pool-VOLs

You can use External Storage to connect your P9500 storage system to multiple other storage

systems. In External Storage terminology, your P9500 storage system is referred to as a local

storage system, and the other multiple storage systems are referred to as external storage systems.

Requirements for Fast Snap tasks 33

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Hp XP P9500 Storage User Manual Page 33

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