HP XP7 Storage - Manual (Page 34)

Fast Snap pair restoration and host server I/O performance
If a problem occurs with a P-VOL due to a failure, you can restore the FS pair so that data in the
P-VOL is returned to a normal condition, the condition it was when you stored snapshot data.
Restoring FS pairs when the workload on the storage system is high can decline host server I/O
performance because the P-VOL replication process starts. Enable the Copy threshold option to
lower the workload on the storage system.
Enabling the copy threshold option temporarily stops the FS replication processes and the following
software:
•
BC
•
BC Z
•
FC Z
•
Auto LUN
As the workload on the XP7 storage system decreases, the replication processes that you stopped
by enabling the copy threshold option restart.
Related topics
•
For more information about the Copy threshold option, see “The copy threshold option and
host server I/O performance” (page 17) .
•
For more information about enabling the copy threshold option, contact HP Technical Support.
•
“Fast Snap pair restoration” (page 15)
•
“Restoring Fast Snap pairs” (page 79) .
Calculating and assigning pool capacity
Use the following formula to calculate the capacity of the snapshot data that you can store in the
pool:
The capacity of the snapshot data that you can store in the pool = the
total capacity of pool-VOLs in the pool - The capacity of V-VOL
management areas
The capacity of V-VOL management areas is 3% of the pool capacity.
Use the following formula to calculate the pool capacity:
The capacity of the pool (MB) = The total number of pages X 42 - 4200
Use the following formula to calculate the total number of pages:
The total number of pages = Sigma (floor (floor (pool-VOL number of
blocks / 512) / 168)) for each pool-VOL
floor( ): Truncates the value calculated from the formula in parentheses after the decimal point.
Estimate pool-VOL capacity in multiples of 42MBs. Specifying a pool-VOL capacity in other multiples
less than 42MBs truncates the fraction.
If you install THP/Smart/FS Extension in the SM, the total capacity of all pools is 12.3PB. The
available pool capacity per P-VOL is 768TB.
Writing data to an area in the P-VOL copies snapshot data to the pool. Any subsequent data
writing to the same area changes the capacity to the capacity of the snapshot data that you want
to copy to the pool. Writing data to the same area more than once decreases the capacity of the
snapshot data that you want to copy to the pool.
34 Planning and design requirements