Initial Copy; Update Copy - Hitachi G200 User Manual

The following figure illustrates the initial copy and update copy operations.

Initial copy

When a new pair is created, the entire contents of the P-VOL are copied to
the S-VOL cylinder 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.
During the create pair operation, 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 affect the speed of data transfer and storage system performance. These
are:
• Copy Pace. You specify the number of tracks that can be copied
simultaneously before the primary 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.
• Maximum Initial Copy Activities. You specify the maximum number of
concurrent initial copies that the system performs.
• Initial Copy Priority. You specify the order in which copying is
performed on multiple pairs. This is used if more pairs are being created
in the operations than the maximum initial copy activity setting.
• Round Trip Time. You specify the time limit for data to travel from P-
VOL to S-VOL. The value is used by the storage system to control initial
copy pace when update copying is in progress.
These options are available on Device Manager - Storage Navigator only.

Update copy

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).
When 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.
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
TrueCopy overview
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