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Hitachi Command Control Interface (CCI) User and Reference Guide 225
4.10.1.3 SVOL-Takeover Function
The SVOL-takeover function allows the takeover node to use the secondary volume (except
in COPY state) in SSUS(PSUS) state (i.e., reading and writing are enabled), on the assumption
that the remote node (possessing the primary volume) cannot be used. The data consistency
of the Hitachi TrueCopy SVOL is evaluated by its pair status and fence level (same as
paircurchk, refer to). If the primary and secondary volumes are not consistent, the SVOL-
takeover function fails. If primary and secondary volumes are consistent, the SVOL-takeover
function attempts to switch to the primary volume using Resync for Swapping. If successful,
the SVOL-takeover function returns Swap-takeover as the return value of the horctakeover
command. If not successful, the SVOL-takeover function returns SVOL-SSUS-takeover as the
return value of the horctakeover command. In case of a host failure, Swap-takeover is
returned. In case of an ESCON/FC or P-VOL site failure, SVOL-SSUS-takeover is returned.
SVOL-takeover can be specified for a paired volume or a group. If the SVOL-takeover is
specified for a group, a data consistency check is executed for all volumes in the group, and
all inconsistent volumes are displayed (see example in Figure 4.24).
Group Pair vol Port targ# lun# LDEV# Volstatus Status Fence To be...
oradb1 /dev/dsk/hd001 CL1-A 1 5 145 S-VOL PAIR NEVER Analyzed
oradb1 /dev/dsk/hd002 CL1-A 1 6 146 S-VOL PSUS STATUS Suspected
Figure 4.24 Display of Inconsistent Volumes for SVOL-Takeover of Group
Note for Hitachi TrueCopy Async/UR: The CCI software on the S-VOL side will issue a
Suspend for Swapping to the S-VOL side RAID storage system. Non-transmitted data of the
P-VOL will be copied to the S-VOL side, and a Resync for Swapping operation will be
performed (after the copy process). In case of a host failure, this data synchronize operation
will be accomplished and SVOL-takeover function will return Swap-takeover by attempting a
Resync for Swapping. In case of an ESCON/FC or P-VOL site failure, this data synchronize
operation may fail. Even so, the SVOL-takeover function will do Suspend for Swapping, and
enable the S-VOL to be used. As result, this function will be returned as SVOL-SSUS-
takeover. Through this behavior, you will be able to judge that the non-transmitted data of
the P-VOL was not transmitted completely when SVOL-takeover returns SVOL-SSUS-
takeover.
The SVOL-takeover operation is required to copy non-transmitted P-VOL data within a given
timeout value (specified by the -t <timeout> option). If the timeout occurs (before SVOL
takeover has completed all S-VOL changes to SSWS state), the horctakeover command will
be failed with EX_EWSTOT. Therefore this timeout value should be a greater than (or equal
to) the start-up timeout value for the HA Control Script.
If the horctakeover command failed due to timeout, then try to recover as follows:
1.
Wait until SVOL state becomes SSWS (use pairdisplay -g <group> -l -fc command), and
try to the start-up again for the HA Control Script.
2.
Make an attempt at doing resynchronize original PVOL based on SVOL using pairresync
-g <group> -swaps -c <size> for Fast Failback Performance. If this operation has been
failed at [EX_CMDRJE] or [EX_CMDIOE], then the cause is ESCON/FC link down and/or
site failure. After the recovery from failure, please try again this command.