HP StorageWorks Storage Mirroring for Linux User's Guide (T2558-96317, June 2009)

10 - 1
Mirroring and
Replication
Mirroring and replication are the key components of Storage Mirroring. This chapter contains
information on the following mirroring and replication capabilities.
 Controlling mirroring on page 10-1
 Controlling an automatic mirror on page 10-3
 Configuring and removing orphan files on page 10-5
 Starting replication on page 10-6
Controlling mirroring
After a connection is established, you need to be able to control the mirroring. You can start, stop,
pause and resume mirroring. Right-click the connection on the right pane of the Management Console
and select Mirroring and the appropriate mirror control.
 Pause or Resume—When pausing a mirror, Storage Mirroring stops queuing mirror data on the
source but maintains a pointer to determine what information still needs to be mirrored to the
target. Therefore, when resuming a paused mirror, the process continues where it left off.
 Stop—When stopping a mirror, Storage Mirroring stops queuing mirror data on the source and
does not maintain a pointer to determine what information still needs to be mirrored to the target.
Therefore, when starting a mirror that has been stopped, the process will mirror all of the data
contained in the replication set.
 Start—If you select to start a mirror, you will need to make the following two selections on the
Start Mirror dialog box.
 Full Mirror—All files in the replication set will be sent from the source to the target.
 Difference Mirror—Only those files that are different based size or date and time (depending
on files or block devices) will be sent from the source to the target. See the table File
Differences Mirror Options Compared on page 10-2 for a comparison of how the file
difference mirror settings work together, as well as how they work with the global checksum
setting on the Source tab of the Server Properties.
 Only send data only if source’s date is newer than the target’s date—Only those
files that are newer on the source are sent to the target.
 Use Checksum to send minimal blocks of data—For those files flagged as different,
the mirror performs a checksum comparison and only sends those blocks that are
different.
 Calculate Replication Set size prior to mirror—Determines the size of the replication set
prior to starting the mirror. The mirroring status will update the percentage complete if the
replication set size is calculated.
NOTE: If you are using a database application, do not use the newer option unless
you know for certain you need it. With database applications, it is critical that
all files, not just some of them that might be newer, get mirrored.