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Online copy – Dell PowerVault MD3200i User Manual

Page 175

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Configuration: Premium Feature—Virtual Disk Copy

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the source virtual disk may be rejected by the storage array RAID controller

modules and result in an error message. Make sure that the Read-Only

attribute for the target virtual disk is disabled after the virtual disk copy is

complete to prevent error messages from being displayed.

Online Copy

An online copy creates a point-in-time snapshot copy of any virtual disk

within a storage array, while still allowing writes to the virtual disk when the

copy is in progress. This is achieved by creating a snapshot of the virtual disk

and using that snapshot as the actual source virtual disk for the copy. In an

online virtual disk copy, the relationship is between a snapshot virtual disk

and a target virtual disk. The virtual disk for which the point-in-time image is

created (the source virtual disk) must be a standard virtual disk in the storage

array.
A snapshot virtual disk and a snapshot repository virtual disk are created

during the online copy operation. The snapshot virtual disk is not an actual

virtual disk containing data; instead, it is a reference to the data contained on

the virtual disk at a specific time. For each snapshot taken, a snapshot

repository virtual disk is created to hold the copy-on-write data for the

snapshot. The snapshot repository virtual disk is used only to manage the

snapshot image.
Before a data block on the source virtual disk is modified, the contents of the

block to be modified are copied to the snapshot repository virtual disk.

Because the snapshot repository virtual disk stores copies of the original data

in those data blocks, further changes to those data blocks write only to the

source virtual disk.

NOTE:

If the snapshot virtual disk that is used as the copy source is active, the

source virtual disk performance degrades due to copy-on-write operations. When

the copy is complete, the snapshot is disabled and the source virtual disk

performance is restored. Although the snapshot is disabled, the repository

infrastructure and copy relationship remain intact.

book.book Page 175 Tuesday, June 18, 2013 3:15 PM

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