HP StorageWorks XP Remote Web Console Software - Manual (Page 28)

Synchronous pairs. The MCU or RCU can suspend XP Continuous Access Asynchronous pairs. For
further information, see
“XP Continuous Access Asynchronous suspension conditions” (page 29) .
The MCU suspends an XP Continuous Access pair when it detects the following suspension
conditions:
•
The MCU detects that you deleted the volume pair from the RCU
•
The MCU detects an error condition related to the RCU, S-VOL, or XP Continuous Access
update copy operation
•
The MCU cannot communicate with the RCU
•
The MCU detects an XP Continuous Access Asynchronous suspension condition
When an XP Continuous Access Sync pair is suspended, the MCU stops performing update copy
operations to the S-VOL and may or may not continue accepting write I/Os for the P-VOL, depending
on the P-VOL fence level pair option. If a synchronous update copy operation fails, the MCU
maintains exact synchronization by reporting a unit check and decommitting the P-VOL update.
The host system and application program regard that write operation to the P-VOL as failed. If the
MCU accepts write I/Os for a suspended P-VOL, the MCU tracks P-VOL cylinders updated while
the pair is suspended. When a suspended sync pair is resumed, the MCU copies out-of-sync P-VOL
cylinders to the S-VOL. XP Continuous Access does not allow access to an S-VOL while the pair is
suspended (only when split).
You must stop host I/Os before suspending XP Continuous Access Synchronous pairs with the Data
fence level and following conditions:
•
XP Continuous Access Synchronous and Asynchronous pairs exist in the same disk array
•
There are host I/Os to the XP Continuous Access Asynchronous pairs
If you do not stop host I/Os, pairs might be forcibly suspended because of a time-out error, and
host I/Os are rejected.
When an XP Continuous Access Asynchronous (XP Continuous Access Async) pair is suspended,
the MCU stops performing XP Continuous Access Async recordset operations for the pair. The
MCU continues accepting write I/Os for the suspended P-VOL and tracks P-VOL cylinders updated
while the pair is suspended. The MCU and RCU also tracks recordsets discarded during the pair
suspension. When a suspended XP Continuous Access Async pair is resumed, the RCU sends the
S-VOL cylinder bitmap to the MCU, and the MCU merges the P-VOL and S-VOL bitmaps to determine
which cylinders are out-of-sync. This method ensures that all cylinders containing recordsets discarded
at the RCU are resynchronized at this time.
A suspended (or split) XP Continuous Access Async S-VOL has an additional status called consistency
status. Consistency status is displayed only at the RCU and indicates the S-VOL's update sequence
consistency with respect to other S-VOLs in the same group. See
“Consistency status descriptions
for split/suspended XP Continuous Access Async S-VOLs” (page 27) for a description of consistency
status for suspended/split XP Continuous Access Async S-VOLs.
Table 9 XP Continuous Access suspend types
Description Applies to Type
The MCU detected an error condition at the RCU causing the
MCU to suspend the XP Continuous Access volume pair. S-VOL
suspend type is PSUE-S-VOL Failure. P-VOL, S-VOL PSUE, by RCU
The MCU detected an error during RCU communications or
update copy. In this case, S-VOL suspend type is usually
PSUE-S-VOL Failure. This suspend type is also used when the
number of paths falls below the minimum number of paths setting
on the RCU Option pane. P-VOL, S-VOL PSUE, S-VOL Failure
28 Overview of XP Continuous Access operations