HP StorageWorks XP Remote Web Console Software - Manual (Page 13)

Figure 2 Remote copy operations
Initial copy operations
Initial copy operation synchronizes P-VOLs and S-VOLs independently of host I/O processes. Initial
copy operations are the same for XP Continuous Access Sync and XP Continuous Access Async
pairs. XP Continuous Access initial copy operations occur when adding a pair (paircreate) or
resuming a split/suspended pair (pairresync). When a new pair is created, the entire contents of
the P-VOL are copied to the S-VOL cylinder by cylinder, except for diagnostic and unassigned
alternate tracks. You can select No Copy for the Initial Copy field of the initial copy parameters,
which copies only cylinder #0 to the S-VOL. If No Copy is selected, you are responsible for ensuring
that P-VOLs and S-VOLs are already identical. The MCU cannot verify the contents of volumes.
When a split/suspended pair is resumed (pairresync), only cylinder #0 and out-of-sync cylinders
(updated by write I/Os during split/suspension) are copied to the S-VOL. When the XP Continuous
Access S-VOL write enable function is used, the RCU tracks S-VOL updates and sends the S-VOL
cylinder bitmap to the MCU when the split pair is resumed. In this case the MCU merges the P-VOL
and S-VOL bitmaps to identify out-of-sync cylinders.
For additional flexibility, XP Continuous Access provides the following options for initial copy:
•
Use the Initial Copy Pace field of the initial copy parameters to specify how many tracks the
XP Continuous Access initial copy operation copies simultaneously when creating/resuming
an XP Continuous Access pair. This option can only be specified using the Remote Web
Console or XP Command View Advanced Edition.
•
Use the Priority field of the initial copy parameters to specify the order in which initial copy
operations are performed when creating/resuming multiple XP Continuous Access pairs. This
option can only be specified using the Remote Web Console.
•
Use the Maximum Initial Copy Activity option to specify maximum number of concurrent initial
copy and resync operations that each MCU can perform (not pair-specific). This option can
only be specified using the Remote Web Console.
Update copy operation
Update copy operations occur when the host issues a write I/O operation to the P-VOL of an
established XP Continuous Access pair. Update copy operations duplicate P-VOL write I/Os at the
S-VOL to keep the volume pair synchronized. XP Continuous Access provides two modes for update
copy operations: synchronous and asynchronous. Update copy mode is specified when you add
an XP Continuous Access pair and is unchangeable for the life of the pair.
For synchronous update copy mode, the MCU ensures the P-VOL and S-VOL are synchronized at
all times. When using fence level “data,” the MCU does not return final ending status for the P-VOL
Remote copy operations 13