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Chapter 26. Global Mirror examples 403
To query the newly created FlashCopy relationships use the command lsflash as described
in 26.11.3, “Query FlashCopy pairs” on page 396.
26.12.4 Verify FlashCopy status between B and C volumes
After a local site failure, you will need to check the status of all FlashCopy pairs that were in
the Global Mirror session.
Let us see how to verify and eventually take some corrective actions on the Global Mirror
FlashCopy pairs at the remote site, when there has been a primary site failure. For a more
detailed discussion on this topic, see 26.4.4, “Check Global Mirror FlashCopy status between
B and C volumes” on page 355 and 23.7.4, “Check for valid Consistency Group state” on
page 285.
To verify the
sequence number and revertible state of the FlashCopy sessions, first use the
command lsflash as described in 26.11.3, “Query FlashCopy pairs” on page 396.
Secondly, execute either the commitflash or the revertflash command, depending on
whether or not the FlashCopy pairs were successfully set to a revertible state, and whether
their sequence numbers are equal or not.
We need to remember that Global Mirror is a distributed solution:
When a Consistency Group is processed, the Master acts as a session manager and does
an incremental revertible FlashCopy on its own recovery site, while at the same time
asking its Subordinates to also perform such a task at their recovery sites.
When a Consistency Group is in progress, several incremental revertible FlashCopy
operations may be running. The FlashCopy process is looking at the change recording bit
map on the B volumes, and is comparing it with the target bit map on the C volumes.
When the incremental FlashCopy is finished, the change recording bit map is cleared and,
therefore, all the changes are committed on the C volumes. The corresponding FlashCopy
pairs are set to a nonrevertible state by the Master.
These are the reasons why one of these four situations could occur:
1. If all FlashCopy pairs are nonrevertible and their sequence numbers are equal, it means
that the Consistency Group process had finished.
There is no action required because the Consistency Group is intact on the C volumes.
2. If some FlashCopy pairs are revertible and their sequence numbers are equal, and others
are not revertible and their sequence numbers are equal but do not match the revertible
FlashCopies sequence number, it means that some FlashCopy pairs are running in a
Consistency Group process and some have not yet started their incremental process.
To preserve the consistency we need to overwrite new data with data saved at the last
consistency formation for the FlashCopy pairs already in the new Consistency Group
process. For this use the revertflash command of the DS CLI.
3. If all FlashCopy pairs are revertible and their sequence numbers are equal, it means that
all the FlashCopy pairs are running in a Consistency Group process and none have
finished their incremental process.
We need to overwrite new data with data saved at the last consistency formation for all the
FlashCopy pairs. For this use the revertflash command of the DS CLI.
Note: At this level, we do not use the command setflashrevertible because Global
Mirror has already issued this command internally.