HP StorageWorks XP Remote Web Console Software - Manual (Page 38)

Table 19 Rough Estimate of the Capacity of a P-VOL to be created
And If the Pool Capacity is If a Shared Memory
is Added to
30,720
GB 20,480
GB 14,336
GB 12,288
GB 10,240
GB 8,192
GB 6,144
GB 4,096
GB 2,048
GB
— — — — — — — 10.5 TB 25.0 TB XP
Snapshot
1
XP24000
Disk
Array
— — — — — — 13.5 TB 28.0 TB 42.0 TB XP
Snapshot
2
— — 13.5 TB 28.0 TB 42.0 TB 56.0 TB 71.0 TB 85.0 TB 100.0
TB XP
Snapshot
3
— 29.0 TB 77.5 TB 92.0 TB 106.0
TB 120.0
TB 134.0
TB 149.0
TB 164.0
TB XP
Snapshot
4
14.0 TB 89.0 TB 141.5
TB 156.0
TB 170.0
TB 184.0
TB 194.0
TB 209.0
TB 224.0
TB XP
Snapshot
5
— — — — — — — 10.5 TB 25.0 TB XP20000 Disk
Array
— Not applicable
Calculating the Number of XP Snapshot Pairs Using the Number of Pair Tables
Pair tables are used by Compatible FlashCopy Version 2 and XP Snapshot pairs in order to store
control information which is needed to manage the pairs. To create a Compatible FlashCopy
Version 2 pair or an XP Snapshot pair, you need one pair table for each pair.
Up to 1,048,575 pair tables are available in one subsystem.
Among storage system program products, only Compatible FlashCopy Version 2 and XP Snapshot
use pair tables. Therefore, if you use Compatible FlashCopy Version 2, the number of available
pair tables for XP Snapshot pairs can be calculated by subtracting the number of differential tables
used by the Compatible FlashCopy Version 2 pairs from the number of pair tables for the whole
subsystem.
For information about how to check the number of pair tables used by Compatible FlashCopy
Version 2 pairs (that is, the number of already created Compatible FlashCopy Version 2 pairs),
see the HP XP24000/XP20000 for FlashCopy Mirroring Software User Guide.
For example, when the number of pair tables used by Compatible FlashCopy Version 2 is 30,000,
the number of XP Snapshot pairs that can be created for a subsystem can be calculated as follows.
Example
1,048,575 – 30,000 = 1,018,575
According to this result, the maximum number of XP Snapshot pairs that can be created is
1,018,575.
Performance Considerations
If XP Snapshot performs a restore operation when the load of the subsystem is heavy, it is more
likely that host server I/O performance (response) may be degraded. The Copy Threshold option
allows you to effectively decrease the load of the subsystem.
38 Preparing for XP Snapshot Operations