IBM Flex System V7000 Expansion Enclosure 4939H29 Manual Do Utilizador
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4939H29
8068ch10-Volume Mirror and Migration.fm
Draft Document for Review January 29, 2013 12:52 pm
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IBM Flex System V7000 Storage Node Introduction and Implementation Guide
10.1 Volume mirroring and migration options
Volume mirroring is a function that is designed to allow a volume to remain online even when
the primary storage pool backing it becomes inaccessible. This function is designed to protect
the volume from storage infrastructure failures by providing seamless mirroring between
different storage pools.
the primary storage pool backing it becomes inaccessible. This function is designed to protect
the volume from storage infrastructure failures by providing seamless mirroring between
different storage pools.
This function is provided by a specific volume mirroring function built into the I/O stack, and
cannot be manipulated like the FlashCopy or other copy service functions. This feature does,
however, enable a migration functionality, which can be obtained by splitting the mirrored copy
from it’s source or by using the
cannot be manipulated like the FlashCopy or other copy service functions. This feature does,
however, enable a migration functionality, which can be obtained by splitting the mirrored copy
from it’s source or by using the
migrate to
command. Volume mirroring does not make use of
or control external back-end storage mirror or replication functions as they are independent of
the IBM Flex System V7000 Storage Node.
the IBM Flex System V7000 Storage Node.
10.1.1 Tunable timeout
Generally, with this feature, the host IO completes when both copies of the volume mirror are
written. This feature has a tunable latency tolerance. This is designed to provide an option to
give preference to losing the redundancy between the two copies. This tunable timeout has
two value settings, either latency or redundancy to chose from.
written. This feature has a tunable latency tolerance. This is designed to provide an option to
give preference to losing the redundancy between the two copies. This tunable timeout has
two value settings, either latency or redundancy to chose from.
The latency tuning option (set by running
svctask chvdisk -mirrowritepriority latency
) is
the default and prioritizes host I/O latency. This setting produces a preference to host I/O over
availability.
availability.
However, you might need to give preference to redundancy when availability is more
important than I/O response time. To accomplish this task, run command
important than I/O response time. To accomplish this task, run command
svctask chvdisk
-mirrowritepriority redundancy
.
Regardless of which option you choose, volume mirroring can provide extra protection for
your environment and ease of management for moving data around to better serve your
needs.
your environment and ease of management for moving data around to better serve your
needs.
10.1.2 Usage of mirroring for migration
With regard to using mirroring for migration, there are several use cases that can exist:
Creating multiple volume images using Volume Mirroring then Split into New Volume: This
is one of the most common uses of this function. This option allows you to use the RAID 1
functionality to create two copies of data that initially have a set relationship (one primary
and one secondary) but then break the relationship (both primary and no relationship) and
make them independent copies of data. You can use this mode to migrate data between
storage pools and devices. You might use this option if you want to move volumes to
multiple different storage pools. You can only mirror one volume at a time.
is one of the most common uses of this function. This option allows you to use the RAID 1
functionality to create two copies of data that initially have a set relationship (one primary
and one secondary) but then break the relationship (both primary and no relationship) and
make them independent copies of data. You can use this mode to migrate data between
storage pools and devices. You might use this option if you want to move volumes to
multiple different storage pools. You can only mirror one volume at a time.
Volume migration using Move to Another Pool: This option allows any volume to be moved
between storage pools without interruption to host access. This option is effectively a
quicker version of clicking Volume Mirroring
between storage pools without interruption to host access. This option is effectively a
quicker version of clicking Volume Mirroring
Split into New Volume. You might use
this option if you want to move volumes in a single step or do not already have a volume
mirror copy.
mirror copy.
Migrating from external storage using Image mode: This option allows you to migrate data
from an already existing volume or LUN on another external storage subsystem into the
IBM Flex System V7000 Storage Node as an image mode mdisk. With this function, the
volume can then be mirrored as a second copy to another already existing generic, striped
from an already existing volume or LUN on another external storage subsystem into the
IBM Flex System V7000 Storage Node as an image mode mdisk. With this function, the
volume can then be mirrored as a second copy to another already existing generic, striped