HP StorageWorks XP Remote Web Console Software - Manual (Page 35)

The MCU suspends an XP Continuous Access pair when it detects any of the following suspension
conditions:
•
When the MCU detects that the user has released the pair from the RCU,
•
When the MCU detects an error condition related to the RCU, the S-VOL, or an XP Continuous
Access update copy operation,
•
When the MCU is unable to communicate with the RCU, or
•
When the MCU detects an XP Continuous Access Asynchronous suspension condition.
When an XP Continuous Access Synchronous 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, so that the host system and application program regard that write operation to the P-VOL
as failed. If the MCU accepts subsequent write I/Os for a suspended P-VOL, the MCU records the
data in the P-VOL tracks that are updated while the pair is suspended as differential data. When
a suspended XP Continuous Access Synchronous pair is resynchronized, the MCU copies the
out-of-sync P-VOL tracks to the S-VOL as differential data. XP Continuous Access does not allow
access to an S-VOL while the pair is suspended (only when split).
When an XP Continuous Access Asynchronous pair is suspended, the MCU stops performing XP
Continuous Access Asynchronous recordset operations for the pair. The MCU continues accepting
write I/Os for the suspended P-VOL and records the data in the P-VOL tracks that are updated
while the pair is suspended as differential data. The MCU and RCU also keep track of any recordsets
that were discarded during the pair suspension as differential data. When a suspended XP
Continuous Access Asynchronous pair is resynchronized, the RCU sends the S-VOL differential
data to the MCU, and the MCU merges the P-VOL and S-VOL differential data to determine which
tracks are out-of-sync. This method ensures that all tracks that contain recordsets that were discarded
at the RCU are resynchronized at this time.
A suspended (or split) XP Continuous Access Asynchronous S-VOL has an additional status called
the consistency status. The consistency status is displayed only at the RCU and indicates the S-VOL’s
update sequence consistency with respect to the other S-VOLs in the same group. See
“Consistency
Status for Split or Suspended XP Continuous Access Asynchronous S-VOLs” (page 34) for a
description of consistency statuses for suspended/split XP Continuous Access Asynchronous S-VOLs.
Table 12 Suspend Types (PSUE)
Description Applies to Type
The MCU detected an error condition at the RCU that caused
the MCU to suspend the XP Continuous Access pair. The S-VOL
suspend type is S-VOL Failure. P-VOL, S-VOL by RCU
The MCU detected an error during RCU communications or
an IO error during update copy. In this case, the S-VOL
suspend type is usually 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 dialog box. P-VOL, S-VOL S-VOL Failure
The MCU could not find valid control information in its
nonvolatile memory during IMPL. This condition occurs only if
the MCU is without power for more than 48 hours (that is,
power failure and fully discharged backup batteries). P-VOL, S-VOL XP
Continuous Access
Async MCU IMPL
The MCU suspended the pair before the initial copy operation
was complete. The data on the S-VOL is not identical to the
data on the P-VOL. P-VOL, S-VOL Initial Copy Failed
Pair Status 35