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Disaster Recovery with DPM 2010 RRS feed

  • Question

  • I have a pretty good handle on what a secondary DPM server is and understand that the backed up data and database is copied from the primary to the secondary. I would like to leverage iSCSI and MPIO when backing up to disk and use the data that I already have on disk and not copy it to the secondary. Is this possible or do I need to carve out more space from my iSCSI based storage for the secondary? Basically I would like to attach the secondary server to the iSCSI based LUN that already exists for the primary and be able to use that data to restore from or backup to in the event of a disaster recovery situation.

    Has anyone attempted to do this or is there a better way?

    Tuesday, November 30, 2010 12:02 AM

Answers

  • Because of the way that DPM is architected I don't believe there is a way to accomplish a single copy of data for both the primary and secondary DPM servers. DPM backup to disk is based on a block level comparison between the data being protected and the (replica) data on the DPM server. The modified blocks are then marked as a change and reorded in a VSS snapshot in the recovery point volume. As a result the primary and secondary DPM servers cannot be looking to the same copy of the (replica) data as there would be no point of reference to determine the block changes that would then happen between protected data and the primary and then primary and secondary - not to mention the issues of an MPIO scenario (or cluster shared volume) where you have two data sources attempting to acces what is meant to be a replica copy of a single data source.

    One of the key points of a primary to secondary DPM server relationship is that in the event of a disaster for the DPM primary - the secondary is able to take over protection of the primaries data sources and continue protection.

    However, if the iSCSI target was to have an underlying technology that could look at the block data at a disk level and perform deduplication that way then you would achieve much the same end as the data on the replica volumes for the primary and secondary would be almost identical. The big risk there is that if you lost the iSCSI target then you would lose all of your disk based recovery points. These techologies also tend to be very expensive and depending on the amount of data being protected - disk may be cheaper.

    The other option you could look at is virtual tape - which to DPM would look like tape but actually create disk files to store on the iSCSI. The benefit here is that you could use the secondary DPM server to restore from those virtual tapes so long as you could attach the virtual tape to the secondary DPM server. The problem with this scenario is that if the primary fails then you would have to configure all of your protection on the secondary and consume that disk, plus you would lose your recovery points.

    Hope this is helpful.

    Tuesday, November 30, 2010 10:16 AM