Hitachi TAGMASTORE MK-90RD011-25 - Manual (Page 46)

28 Chapter 2 Overview of CCI Operations
2.4.2.3 TrueCopy Async/Universal Replicator ERROR State
In the case of an ESCON or fibre-channel (FC) failure, the S-VOL FIFO queue is missing a data
block that was transferred from the P-VOL FIFO queue. The RCU waits to store the next
sequenced data block in the S-VOL FIFO queue until the TrueCopy Async copy pending
timeout occurs (defined using Hitachi TrueCopy remote console software). If the timeout
occurs during this waiting state, the pair status is changed from PAIR to PSUE, and non-
sequenced data blocks are managed by the S-VOL bitmap. The missing data block can be
recovered using the pairresync command, which merges the S-VOL bitmap with the P-VOL
bitmap, shows its situation on the secondary side.
BITMAP Secondary
volume
BITMAP
FIFO (sidefile)
Secondary
volume
RCU (secondary)
PSUE
PAIR
Asynchronous transfer
1
2
3
5
4
ESCON ® /fibre failure
5 3 2 . . . . . . 1
Figure 2.11 Hitachi TrueCopy Async Suspension Condition
2.4.3 TrueCopy Sync/Async and Universal Replicator Fence-Level Settings
Hitachi TrueCopy volume pairs are assigned a fence level for write I/Os to ensure the
mirroring consistency of critical volumes. Accordingly, when the secondary volume takes
over from the primary volume, the takeover action is determined according to the pair
status and fence level of the corresponding secondary volume. Table 2.7 shows the
relationship between Hitachi TrueCopy pair status and fence level.