Справочник Пользователя для IBM Flex System V7000 Expansion Enclosure 4939H29

Draft Document for Review January 29, 2013 12:52 pm

IBM Flex System V7000 Storage Node Introduction and Implementation Guide

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.

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 

 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. 

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. 

The latency tuning option (set by running 

) is 

the default and prioritizes host I/O latency. This setting produces a preference to host I/O over 
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 

.

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.

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.

��

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



 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.

��

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