User guide

NOTE: Even if the restore process is not in progress, the pair status can change to “PSUE”
when a failure occurs.
• The pool usage rate reaches 100 percent.
The status of FS pairs depends on whether the hosts can read from or write to the FS pair P-VOL
or S-VOLs.
The following table explains the host access and pair status.
S-VOLP-VOLFS pair status
WriteReadWriteRead
NoNoYesYesSMPL
NoNoYesYesSMPL(PD)
NoNoYesYesCOPY
NoNoYesYesPAIR/PFUL
YesYesYesYesPSUS/PFUS
NoNoYesYesRCPY
NoNoYesYesPSUE
Legend
Yes: Hosts can access the volume
No: Hosts cannot access the volume
CAUTION: If a host uses a software application to monitor FS pair volumes, the software
application can abnormally terminate depending on the status of a S-VOL. For example, a monitoring
application can terminate abnormally if access from the application is rejected, because S-VOLs
in a status other than “PSUS” and “PFUS” reject access from hosts.
If a host connects to two or more ports, an abnormality can occur with ports that are not connected
to S-VOLs rejecting access from hosts. To resolve these issues, terminate the software application
that monitors volumes.
Copy threshold option
Use the copy threshold option to help minimize the decline of host server I/O performance. The
host server I/O performance can decrease as the workload on the storage system increases. If
you restore FS pairs when the workload on the storage system is high, replication processes for
the P-VOLs begin.
During the replication processes, the host server I/O performance can decrease and the workload
on the storage system can become excessively heavy. You can temporarily stop the FS replication
processes and the following software by enabling the copy threshold option:
• BC/SS
• BC Z
• Compatible FlashCopy (FC Z)
• Auto LUN
• SS
As the workload on the storage system decreases, the replication processes that were stopped by
the copy threshold option restart.
16 Overview of Fast Snap