Hitachi Command Control Interface (CCI) User and Reference Guide 291
4.15 Synchronous Waiting Command (Pairsyncwait) for Hitachi TrueCopy Async/UR
More robust systems need to confirm the data consistency between the Hitachi TrueCopy
Async/UR PVol and SVOL. In DB operations (e.g., Oracle), the commit() of DB transaction
(see Figure 4.70) is needed to confirm that a last wr
iting for the commit() on a local site
reached to remote site by using CCI-unique API command. The pairsyncwait command is
used to confirm that required writing was stored in DFW area of RCU, and it will be able to
confirm whether or not a last writing of just before this command is reached to RCU DFW
area.
When a client issued the pairsyncwait command, this command is placed on the queue
buffer for waiting in the HORCM daemon as a command request. HORCM get the latest
sequence # from MCU sidefile and the sequence # whose block was transferred and stored in
DFW area of RCU with data consistency, and will compare the latest sequence # of MCU
sidefile with the sequence # of RCU DFW area within the term. HORCM replies return code to
this command, when the write of MCU sidefile was stored in RCU DFW area. In use this
function, a client will be able to confirm that a commit() has been reached to remote site,
and also the backup utility on a remote site will be able to split the cascading ShadowImage
volumes (TrueCopy Async/UR
Æ TrueCopy Async/ShadowImage/UR) without splitting for
TrueCopy Asynchronous/UR.
R/W
resynchronization
Asynchronous transfer
Process-A
write(1)
.
write(4)
pairsyncwait
Process-B
write(2)
.
write(3)
HA software package
BIT MAP
Primary
volume
PAIR
PSUS / PSUE
BIT MAP
. . . . . . . . . 5 4 3
FIFO
Primary
volume
BIT MAP
Secondary
volume
BIT MAP
. . . . . . . . . . . 2 1
FIFO
Secondary
volume
CT group
Hitachi RAID Hitachi RAID
PSUE PSUE
PAIR
Note: Write() shows that synchronous
writing or commit() of DB is used.
sequence #
of MCU sidefile
sequence #
of RCU DFW
Figure 4.70 Synchronization for Hitachi TrueCopy Async/UR
