HP XP Continuous Access Software - Manual (Page 28)

28 Continuous Access XP for the XP1024/XP128
Table 7 describes the consistency status for split or suspended Continuous Access XP Async S-VOLs
(consistency status is displayed only at the RCU).
Continuous Access XP suspend types
Table 8 describes Continuous Access XP suspend types, which indicate the reason for suspension. Only
the MCU can suspend Continuous Access XP Synchronous pairs. The MCU or RCU can suspend
Continuous Access XP Asynchronous pairs. For further information, see ” Continuous Access XP Asynchronous
suspension conditions” on page 29 .
The MCU suspends a Continuous Access XP 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 Continuous Access XP update copy
operation
• The MCU cannot communicate with the RCU
• The MCU detects a Continuous Access XP Asynchronous suspension condition
When a Continuous Access XP 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. Continuous
Access XP does not allow access to an S-VOL while the pair is suspended (only when split).
You must stop host I/Os before suspending Continuous Access XP Synchronous pairs with the Data fence
level and following conditions:
• Continuous Access XP Synchronous and Asynchronous pairs exist in the same disk array
• There are host I/Os to the Continuous Access XP 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.
Table 7 Consistency status descriptions for split/suspended Continuous Access XP Async S-VOLs
Consistency status
(displayed at RCU)
Description
Volume Continuous Access XP Asynchronous volume pair was probably split or suspended
alone. Update sequence consistency between this S-VOL and other S-VOLs in this
consistency group is not ensured. This S-VOL cannot be used for disaster recovery at the
secondary site. This status is indicated when:
• You split this pair using the Suspend Range-LU pairsplit-r option.
• This pair was suspended due to a failure that did not affect the entire consistency
group, and the Error Level pair option for this pair is set to LU.
Group Continuous Access XP Asynchronous volume pair was split or suspended with other
pairs in its consistency group. Update sequence consistency between this S-VOL and
other S-VOLs in this consistency group is ensured. This S-VOL can be used for disaster
recovery at the secondary (remote) system (after deleting the
Continuous Access XP
Async pair from the RCU). This status is indicated when:
• You split this pair using the Suspend Range-Group pairsplit-r option.
• All pairs in this consistency group were suspended due to a failure that affected the
entire consistency group, not just one pair (for example, MCU-RCU communication
failure).
• One pair in the group was suspended due to a failure that did not affect the entire
group, and the
Error Level pair option for this pair is set to Group .