Dell PowerVault MD3260 Administrator's Guide - Page 144

Automatically Resynchronizing Virtual Disks

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Automatically Resynchronizing Virtual Disks When automatic resynchronization is selected, the RAID controller module owning the primary virtual disk automatically starts resynchronizing the data on the remote replication pair immediately after communication is restored. NOTE: When choosing automatic resynchronization, a possible loss of data can occur if a resynchronization is interrupted in progress. Since another resynchronization begins automatically after communication is restored between the primary virtual disk and the remote virtual disk, data integrity could be affected. With automatic resynchronization set, you cannot add a secondary virtual disk to a write consistency group. Therefore, write consistency during the resynchronization process is not preserved. The write order is not consistent until the entire group achieves Optimal status. Manually Resynchronizing Virtual Disks When manual resynchronization is selected, you must manually resynchronize and resume the data transfer on a remote replication after communication is restored between the primary and remote virtual disks. Manual resynchronization is the recommended setting for all remote replications for these reasons: • You determine when resynchronization starts, which allows you to better manage and/or mitigate impact on I/O performance. • In a disaster recovery situation, manual resynchronization offers the best chance of retrieving valid data. • When the secondary virtual disk is in a write consistency group, manual resynchronization preserves the write order. Reversing Roles Between The Primary And Secondary Virtual Disks Reversing the roles between the virtual disks promotes the secondary virtual disk to the role of primary virtual disk and demotes the primary virtual disk to the role of secondary virtual. If the primary virtual disk in a remote virtual disk replication fails, you can reverse the roles of the primary virtual disk and the secondary virtual disk to transfer the data back to the restored virtual disk. CAUTION: A potential loss of data access can occur if you reverse roles between the secondary virtual disk and the primary virtual disk while a virtual disk copy is in progress. The role reversal may succeed, but the virtual disk copy fails and cannot be restarted. • You cannot perform a virtual disk copy on a secondary virtual disk in a virtual disk remote replication. To create a virtual disk copy of a secondary virtual disk, you must reverse the roles of the secondary virtual disk and the primary virtual disk, then perform the virtual disk copy on the new primary virtual disk. • While a virtual disk remote replication is synchronizing, you cannot perform a virtual disk copy on either the primary or secondary virtual disk. • If you reverse roles between a secondary virtual disk with less capacity than the primary virtual disk, the role reversal succeeds but the usable capacity of the new primary virtual disk equals the total capacity of the secondary virtual disk. Promoting The Secondary Virtual Disk Or Demoting The Primary Virtual Disk To promote the secondary virtual disk to the role of primary virtual disk, or demote the primary virtual disk to the role of secondary virtual disk: 144

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Automatically Resynchronizing Virtual Disks
When automatic resynchronization is selected, the RAID controller module owning the primary virtual disk automatically
starts resynchronizing the data on the remote replication pair immediately after communication is restored.
NOTE:
When choosing automatic resynchronization, a possible loss of data can occur if a resynchronization is
interrupted in progress. Since another resynchronization begins automatically after communication is restored
between the primary virtual disk and the remote virtual disk, data integrity could be affected.
With automatic resynchronization set, you cannot add a secondary virtual disk to a write consistency group. Therefore,
write consistency during the resynchronization process is not preserved. The write order is not consistent until the
entire group achieves
Optimal
status.
Manually Resynchronizing Virtual Disks
When manual resynchronization is selected, you must manually resynchronize and resume the data transfer on a remote
replication after communication is restored between the primary and remote virtual disks. Manual resynchronization is
the recommended setting for all remote replications for these reasons:
•
You determine when resynchronization starts, which allows you to better manage and/or mitigate impact on I/O
performance.
•
In a disaster recovery situation, manual resynchronization offers the best chance of retrieving valid data.
•
When the secondary virtual disk is in a write consistency group, manual resynchronization preserves the write
order.
Reversing Roles Between The Primary And Secondary Virtual Disks
Reversing the roles between the virtual disks promotes the secondary virtual disk to the role of primary virtual disk and
demotes the primary virtual disk to the role of secondary virtual. If the primary virtual disk in a remote virtual disk
replication fails, you can reverse the roles of the primary virtual disk and the secondary virtual disk to transfer the data
back to the restored virtual disk.
CAUTION: A potential loss of data access can occur if you reverse roles between the secondary virtual disk and
the primary virtual disk while a virtual disk copy is in progress. The role reversal may succeed, but the virtual disk
copy fails and cannot be restarted.
•
You cannot perform a virtual disk copy on a secondary virtual disk in a virtual disk remote replication. To create
a virtual disk copy of a secondary virtual disk, you must reverse the roles of the secondary virtual disk and the
primary virtual disk, then perform the virtual disk copy on the new primary virtual disk.
•
While a virtual disk remote replication is synchronizing, you cannot perform a virtual disk copy on either the
primary or secondary virtual disk.
•
If you reverse roles between a secondary virtual disk with less capacity than the primary virtual disk, the role
reversal succeeds but the usable capacity of the new primary virtual disk equals the total capacity of the
secondary virtual disk.
Promoting The Secondary Virtual Disk Or Demoting The Primary Virtual Disk
To promote the secondary virtual disk to the role of primary virtual disk, or demote the primary virtual disk to the role of
secondary virtual disk:
144