Xp snapshot mechanism – HP StorageWorks XP Remote Web Console Software User Manual
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Figure 1 XP Snapshot mechanism
on page 8, Data A is stored in the XP Snapshot pair's P-VOL. When the host requests to
update Data A to Data B, XP Snapshot copies Data A to the pool volume (pool-VOL) in the pool before
updating the P-VOL. After the copy operation for Data A is complete, XP Snapshot writes Data B to
the area where Data A was stored in the P-VOL, and the P-VOL is updated. From the S-VOL, you can
access Data B in the P-VOL and Data A in the pool-VOL.
XP Snapshot and XP Business Copy are similar because both create pairs. However, XP Snapshot
pair S-VOLs do not consume array capacity because the S-VOLs are actually virtual volumes. Therefore,
XP Snapshot reduces the capacity the array uses as a whole.
The copy process for XP Business Copy pairs takes longer because all P-VOL data is copied to the
S-VOL. On the other hand, the copy process for XP Snapshot pairs takes less time compared to the
copy process for XP Business Copy pairs because, as you can see in
updated P-VOL data is copied to the pool-VOL. The same data in the P-VOL can be referenced by
accessing the XP Snapshot pair's S-VOL, but the actual data does not exist in the S-VOL. The P-VOL
data can be referenced using the S-VOL.
As described previously, XP Snapshot requires less capacity in the array and less copy processing
time compared to XP Business Copy. HP recommends using XP Snapshot to copy and manage data
in the short term with reduced costs. However, XP Snapshot only copies some of the P-VOL data.
Therefore, data stored in the S-VOL is not guaranteed in the following:
•
When a physical failure occurs in a P-VOL
•
When a pool is blocked
On the other hand, XP Business Copy copies all P-VOL data to the S-VOL. Therefore, even if a physical
failure occurs in a P-VOL, you can recover the P-VOL data using the S-VOL data. XP Business Copy
provides higher integrity than XP Snapshot. HP recommends using XP Business Copy when data
Overview of copy solutions
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