HP XP P9500 Storage - Manual (Page 14)

NOTE:
•
If you manipulate volumes (not journals) to create or resynchronize two or more data volume
pairs within the same journal, the base journal data for these pairs will be stored in the restore
journal. Therefore, the operation for restoring the latter base journal will be delayed.
•
You can specify None as the copy mode for initial copy operations. If the None is specified,
initial copy operations are not performed. Therefore, if you specify None, you are responsible
for ensuring that the data in the primary and secondary data volume is exactly the same.
•
You may create a Continuous Access Journal data volume pair by using Continuous Access
Synchronous initial copy. In that case, set the appropriate system option that is system option
474, on both primary and secondary storage system. In addition, the script, which is written
especially for this operation, is also required. If you use the script without setting the system
option on the secondary storage system, the storage system recognizes the Continuous Access
Synchronous R-VOL as the Continuous Access Journal S-VOL, and the SSB log (SSB=CBED) is
generated in the secondary storage system. In this case, the command to create the pair is
rejected. The script is executed normally when you use the script without setting the system
option on the primary storage system, however, note that the processing speed of the
Continuous Access Synchronous initial copy slows down if there is the update I/O during the
operation.
•
If you delete all Continuous Access Journal data volume pairs in the journal and then create
a Continuous Access Journal data volume pair, wait for one or more minutes after deleting
pairs.
•
When an RCU is shared with multiple MCUs, perform the pair resume operation after system
option mode 593 is set to available if you resume 1025 or more pairs from multiple MCUs
(range: mirror) at the same time. Pair resume operations may fail if system option mode 593
is not available.
Update copy operation
When a host produces new or changed information, the following occurs in the primary storage
system:
•
The update is written to the P-VOL.
•
The update is copied to the master journal along with metadata that includes sequence and
other consistency information.
Replication to the secondary system is prompted by the read-journal command. This is issued
by the remote system independently of host I/O activity. Read-journal commands are repeated
every 30 seconds. At this time, the following occurs:
◦ Any data that exists in the master journal on the primary side is sent to the restore journal
on the remote system.
◦ The updated data is then copied to the S-VOL.
◦ Data is updated to the remote system continuously until there is no more data in the master
journal.
◦ Journal data on the primary and secondary systems is discarded when data consistency
is established in the copy.
NOTE: Journal data is transferred using special I/O operations initiated by the secondary
system (RCU), called RIO (remote I/O). RIO provides the most efficient type of data transfer.
Make sure that your channel extenders are capable of supporting RIO. Contact HP Technical
Support for more information.
If an update copy operation fails, the remote system suspends the affected pair or all Continuous
Access Synchronous pairs in the journal. This is dependent on the type of failure. The suspended
14 Continuous Access Journal overview