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Dell PowerVault MD3600f/MD3620f Remote Replication Functional Guide

Database Consistency and Database Hot Backups

After suspending AWOC for database virtual disk replication, and, if a disaster occurs while resuming

RR then the remote database virtual disks are not recoverable. This is due to the delta log processing

of missing I/O in non-original write order. Once RR's resume operations are complete, the virtual disk

pairs are once again in synchronization, and the remote database virtual disks are recoverable in

disaster recovery processing.

In order to have usable database virtual disks in the event that a disaster occurs in the middle of a

resume operation, it is important to snapshot the remote database virtual disks at the very instant that

they are suspended and before the replication is resumed and uses the delta log to re-synchronize.

This requires the auto-resume feature to be turned off and a snapshot is taken at the time of

suspension.

Once the resume operation completes, a second snapshot is taken. This provides the ability to recover

from a primary site disaster. If a disaster occurs during resume operations, the first snapshot is used for

recovery. Once the resume operation completes, the second snapshot is used for recovery.

In both cases, either snapshot will be database consistent and usable for database recovery in the

event of a disaster. We can achieve this using Database Hot Backups.

All databases provide a hot backup operation that allows a storage array to snapshot the database

virtual disks to create a point-in-time copy for backup and/or recovery purposes.

Database hot backups perform a number of functions that ensure recoverability using snapshots or

copies of the database virtual disks. First, the database internal data (pointers, buffers, tablespace data,

and recovery information) are all persisted to the database virtual disks. Enough information is

therefore stored to ensure a successful recovery using the database virtual disks including the

important logs.

Disaster Recovery using RR will use this same hot backup operation to create a remote snapshot of

the database virtual disks. In essence, the remote snapshot is identical to the local snapshot.

During this hot backup window we will use RR's suspend feature to flush the data written on the

primary site virtual disks to their replication counter parts on the remote system; we can then take a

snapshot of the remote virtual disks to create a recoverable set of database virtual disks. RR will then

resume and the database will exit hot backup mode.

NOTE

Periodically performed, this process will create recovery snapshots (also called Recovery

Points) which can be used as remote backup images, or to reprovision the database itself (a second

copy residing at the remote site), and in the event of a disaster and the current set of virtual disks are

not recoverable, the last recovery snapshot will be used instead

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