Volume Mirroring And Migration Options - IBM Storwize V5010 Manual

10.5 Volume mirroring and migration options

Volume mirroring
even when the storage pool that is backing it becomes inaccessible. Volume mirroring is
designed to protect the volume from storage infrastructure failures by seamless mirroring
between storage pools.
Volume mirroring is provided by a specific volume mirroring function in the I/O stack, and it
cannot be manipulated like a FlashCopy or other types of copy volumes. However, this feature
provides migration functionality, which can be obtained by splitting the mirrored copy from the
source, or by using the
mirroring or replication.
With volume mirroring, host I/O completes when both copies are written, and this feature is
enhanced with a tunable latency tolerance. This tolerance provides an option to give
preference to losing the redundancy between the two copies. This tunable timeout value is
Latency or Redundancy.
The Latency tuning option, which is set with chvdisk -mirrowritepriority latency, is the
default. It prioritizes host I/O latency, which yields a preference to host I/O over availability.
However, you might need to give preference to redundancy in your environment when
availability is more important than I/O response time. Use the chvdisk -mirror
writepriority redundancy command to set the redundancy option.
Regardless of which option you choose, volume mirroring can provide extra protection for
your environment.
Migration offers the following options:
Export to Image mode. By using this option, you can move storage from managed mode to
image mode, which is useful if you are using the IBM Storwize as a migration device. For
example, vendor A's product cannot communicate with vendor B's product, but you must
migrate existing data from vendor A to vendor B. By using Export to image mode, you can
migrate data by using Copy Services functions and then return control to the native array
while maintaining access to the hosts.
Import to Image mode. By using this option, you can import an existing storage MDisk or
logical unit number (LUN) with its existing data from an external storage system without
putting metadata on it so that the existing data remains intact. After you import it, all copy
services functions can be used to migrate the storage to other locations while the data
remains accessible to your hosts.
Volume migration by using volume mirroring and then by using Split into New Volume. By
using this option, you can use the available RAID 1 functionality. You create two copies of
data that initially has a set relationship (one volume with two copies, one primary and one
secondary) but then break the relationship (two volumes, both primary and no relationship
between them) to make them independent copies of data.
You can use this to migrate data between storage pools and devices. You might use this
option if you want to move volumes to multiple storage pools. Each volume can have two
copies at a time, so you can add only one copy to the original volume, and then you must
split those copies to create another copy of the volume.
Volume migration by using move to another pool. By using this option, you can move any
volume between storage pools without any interruption to the host access. This option is a
quicker version of the "Volume Mirroring and Split into New Volume" option. You might use
this option if you want to move volumes in a single step, or you do not have a volume
mirror copy already.
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Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.1
is a simple RAID 1-type function that enables a volume to remain online
migrate to
function. Volume mirroring cannot control backend storage