HP StorageWorks XP Remote Web Console Software - Manual (Page 10)

Data A has completed, Data B will be written to the part where Data A was stored in the P-VOL, and the
P-VOL will be updated. From the S-VOL, you can access Data B in the P-VOL and Data A in the pool-VOL.
XP Snapshot and Business Copy are similar because both program products create pairs. However,
S-VOLs of an XP Snapshot pair do not consume the capacity of the storage system because the S-VOLs
are actually virtual volumes. Therefore, XP Snapshot reduces the capacity used by the storage system
as a whole.
The copy process for a Business Copy pair will take a longer time because all data in the P-VOL is
copied to the S-VOL. On the other hand, the copy process for an XP Snapshot pair will take less time
compared to the copy process for Business Copy because, as you can see in the figure above, only the
updated part of the P-VOL is copied to the pool-VOL. The same data in the P-VOL can be referred to by
accessing the S-VOL of the XP Snapshot pair, but the actual data does not exist in this S-VOL. The data
in the P-VOL can be referred to via the S-VOL.
As described above, XP Snapshot requires less capacity of the storage system and less time for copy
processing compared to Business Copy. HP encourages the use of XP Snapshot if you want to copy and
manage the data in a short time with a reduced cost. However, only some of the data in a P-VOL is
copied by XP Snapshot. Therefore, the data stored in an S-VOL is not guaranteed in the following cases:
• When a physical failure occurs in a P-VOL
• When a pool is blocked
On the other hand, Business Copy copies all data of a P-VOL to an S-VOL. Therefore, even if a physical
failure occurs in a P-VOL, you can recover the data of the P-VOL by using the data of the S-VOL. Business
Copy provides higher integrity than XP Snapshot. HP encourages you to consider the use of Business
Copy when data integrity is more important than the speed of the copy process or the capacity of the
storage system.
Overview of HP StorageWorks XP Snapshot 10