HP XP Continuous Access Software - Manual (Page 339)

HA Failover and failback 339
SVOL_PSUS) between P-VOL and S-VOL may need to handled by HA
control scripts.
Async-CA specific behavior
Before the S-VOL is changed to SSUS, an SVOL-takeover will try to copy
non-transmitted data, which remains in the FIFO queue (sidefile) of the
P-VOL, to the S-VOL side.
In the case of an ESCON/FC link failure, this data synchronize operation
may fail. Even so, the SVOL-takeover function performs the force split to
SSUS, and enables usage of the secondary volume.
Non-transmitted data, which remains in the FIFO queue (sidefile) of the
P-VOL, will be moved to a BITMAP to empty the FIFO queue, and the pair
state will be set to PSUE.
Caution
Ordering information regarding the non-transmitted data that is moved to
a BITMAP will be lost. The data represented in the bitmap can be
resynchronized (lost) as the new S-VOL by issuing pairresync –swaps for
recovery from a SVOL-SSUS-takeover at the takeover site (Host B).
Recovery from a SVOL-SSUS-takeover
After the recovery of the ESCON/FC link, this special state (PVOL_PSUE
and SVOL_PSUS) will be changed to COPY state. Thus, the original
S-VOL becomes the NEW_PVOL and overwrites the NEW_SVOL, by
issuing the pairresync –swaps command at the takeover site (Host B).