HP XP P9000 Continuous Access Synchronous for Mainframe Systems User Guide

Initial copy
When a new pair is created, the entire contents of the P-VOL are copied to the S-VOL by cylinder
or by track (this does not include diagnostic and unassigned alternate tracks. The initial copy
synchronizes the P-VOL and S-VOL independently of host I/O processes.
In an initial copy, you can elect to have no data copied if data in the P-VOL and S-VOL are already
identical. You can also specify options that provide additional flexibility between the speed of
data transfer and storage system performance.
• The copy pace option allows you to specify the number of tracks that can be copied
simultaneously before the main system accepts another host request for that P-VOL. If more
tracks are copied, the operation completes quicker; if fewer tracks are copied, performance
is maintained at a higher level.
• The priority option allows you to specify the order in which copying is performed on multiple
pairs. This is used if more pairs are being created than the maximum initial copy activity
setting.
• The maximum initial copy activity option allows you to specify the maximum number of
concurrent initial copy and resync copy operations that each main system performs (not pair
specific).
• The Round Trip Time option allows you to specify the time limit for data to travel from P-VOL
to S-VOL. This value is used by the storage system to control initial copy pace when update
copying is in progress.
These options are available on Remote Web Console. Copy pace is also available using RAID
Manager.
Update copy
If the host issues an update after the initial copy is complete, the data is written to the P-VOL and
copied to the S-VOL. Subsequent updates are held until the current update is completed in both
volumes. This keeps the pair synchronized.
Update copy has a higher priority than initial copy. However, if an initial copy is in progress when
updates are sent by the host, the update copy must wait until the initial copy’s copy pace completes.
For example, if the copy pace is 15 tracks, the update copy may wait up to 15 tracks (1 cylinder).
12 Continuous Access Synchronous Z overview