Initial copy operations, Update copy operations – HP StorageWorks XP Remote Web Console Software User Manual
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Initial Copy Operations
The initial copy operation synchronizes the M-VOL and R-VOL independently of host I/O processes. The
initial copy operation is the same for TC390 Synchronous and TC390A pairs. A TC390 initial copy
operation takes place when you add a new pair or resume a suspended pair. When a new pair is
established, the entire contents of the M-VOL are copied to the R-VOL cylinder by cylinder, including the
VTOC (volume table of contents) but not including the diagnostic and unassigned alternate tracks. For new
pairs, you can also select No Copy or None for the initial copy mode, which copies only the VOLSER
(volume serial number) to the R-VOL. If No Copy or None is selected, the user is responsible for ensuring
that the M-VOL and R-VOL are already identical. The MCU cannot verify the contents of the volumes. When
a suspended pair is resumed (also called a resync operation), only the VOLSER and out-of-sync cylinders
(updated by write I/Os while the pair was suspended) are copied to the R-VOL.
For additional flexibility, TC390 provides the following options for the initial copy operation:
•
Use the number of tracks option to specify how many tracks are copied simultaneously by the TC390
initial copy operation when adding/resuming a TC390 pair. This option can be specified using TC390
through Command View XP or XP Remote Web Console (Add Pair-Option) and the CESTPAIR TSO
command (PACE parameter).
•
Use the Initial Copy Parameters: Priority option to specify the order in which the initial copy operations
are performed when adding/resuming multiple TC390 pairs. This option can only be specified using
TC390 through Command View XP or XP Remote Web Console (Add Pair).
•
Use the Maximum Initial Copy Activities option to specify the maximum number of concurrent initial
copy operations that each MCU can perform (not pair-specific). This option can only be specified using
TC390 through Command View XP or XP Remote Web Console (RCU Option window).
Update Copy Operations
A TC390 update copy operation occurs when the host issues a write I/O operation to the M-VOL of a
TC390 pair. The update copy operation duplicates the M-VOL write I/O at the R-VOL to keep the M-VOL
and R-VOL synchronized. TC390 provides two modes for update copy operations: synchronous and
asynchronous. The update copy mode is specified when you add a TC390 pair and cannot be changed.
TC390 can also specify whether the cache-fast-write (CFW) data is included in the update copy
operations.
For synchronous update copy mode, the MCU ensures that the M-VOL and R-VOL are synchronized at all
times. The MCU does not return device-end status for the M-VOL write I/O until both the M-VOL write and
its associated update copy operation at the RCU are complete. For synchronous mode, the MCU starts the
update copy operation when it receives one of the following:
•
The last write command in the current domain, specified by the preceding locate record command.
•
A write command that requires switching to the next track.
•
A write command that was not preceded by a locate record command.
NOTE:
If many consecutive records are updated by a single CCW chain that does not use the locate
record command (for example, long sequential chained write operations), disk array performance may be
significantly impacted.
For asynchronous update copy mode, the MCU stores the M-VOL updates along with additional control
information in cache, and sends the updates and control information to the RCU completely independent
of the host I/O processes. These updates with their associated control information are called TC390A
recordsets. The RCU stores the TC390A recordsets in cache and performs the updates to the R-VOLs in the
same order as they were performed at the MCU(s) according to the TC390A time-stamp and sequence
information. For more information on TC390A recordset operations, see ”
Priority of initial and update copy: In both TC390 Synchronous and TC390A, update copy has higher
priority than initial copy. However, initial copy is executed based on the copy pace (3 or 15 tracks),
therefore, update copy must wait this interval if initial copy is being executed. For example, if the copy
pace is 15 tracks, the update copy may wait up to 15 tracks (1 cylinder). In the case of TC390A, update