16-10 Dell PowerVault 720N, 740N, and 760N System Administrator and Command Reference Guide
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The following prerequisites must be met before you can replicate a volume:
You must purchase the SnapMirror license. If the source volume and the mirror
are on different filers, you must purchase a license and enter the SnapMirror
license code for each filer. Refer to Enabling Services in Chapter 2 for informa-
tion about how to enter a license code.
You must create an off-line volume to be used as the mirror. SnapMirror does not
automatically create a volume. Refer to Creating Volumes in Chapter 3 for
information about how to create a volume; refer to Making a Volume Inactive in
Chapter 3 for information about how to take a volume off-line.
The source volume must be on-line. Refer to Reactivating an Off-line Volume in
Chapter 3 for information about how to put a volume on-line.
The source volume must not be a mirror.
The capacity of the mirror must be greater than or equal to the capacity of the
source volume. The configuration of the volumes, however, can be different. For
example, the RAID group size can be different for the two volumes. Refer to
Adding Disks to a Volume in Chapter 3 for information about how to add disks
to a volume.
The mirror must not be the root volume.
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Each filer supports up to four simultaneous volume copy operations. For information
about volume copy operations, refer to Number of Volume Copy Operations Snap-
Mirror Generates.
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SnapMirror creates snapshots in the source volume, which are copied to the mir-
ror. Do not delete these snapshots because incremental changes to the mirror
depend on the snapshots. If the filer cannot find the required snapshot, it cannot
perform incremental changes to the mirror.
Refer to Snapshots Created During Data Replication for an example about how
snapshots are created on both the source volume and the mirror.
The mirror must have snapmirrored status. Do not disable the snapmirrored sta-
tus using the volume options command. Otherwise, the mirror becomes a
regular, writable volume. Disable the snapmirrored status only when you no
longer need to mirror incremental changes from the source volume.
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Follow these recommendations to minimize confusion or to replicate data efficiently:
When specifying the mirror update schedule in the /etc/snapmirror.conf file, stag-
ger the update times instead of starting multiple mirror updates at the same