Wednesday, December 7, 2011

How-To: Enabling Data Co-Location on DPM

Microsoft's Data Protection Manager (DPM) 2010 allows backup administrator to co-locate protection groups on tape. In previous version of DPM, tape co-location is not available. This means to say that if you have a protection group with backup size maybe 2Gb a day and 5 LTO4 tapes and the backup strategy is to backup 5 days a week. You will end up with DPM 2010 uses each LTO4 1.6GB (compress) to backup your 2GB everyday. This only utilize 0.1% of your tape capacity, and the worst is that other protection group will not be able to write on the same tape.

With tape co-location available now you can optimizes the tape usage in case you have many small protection groups. The backup to tape will backup multiple protection group on the same tape depending on the backup strategy you configured and consideration on "TapeWritePeriodRatio" and "ExpiryToleranceRange".

Enabling Data Co-Location on DPM
  1. Open DPM Management Shell.
    Set-OptimizeTapeUsage to True using the Set-DPMGlobalProperty cmdlet.
    Set-DPMGlobalProperty -DPMServerName <name of DPM server> -OptimizeTapeUsage $True


Take note that a dataset will be collocated only if both the below conditions are true.

The expiry date of the current dataset should fall in between the following dates: 
Upper bound: furthest expiry date among all the datasets on the tape - (furthest expiry date among all the datasets on the tape - current date) * ExpiryToleranceRange
Lower Bound: furthest expiry date among all the datasets on the tape + (furthest expiry date among all the datasets on the tape - current date) * ExpiryToleranceRange.

Current time should be less than first backup time of the dataset on the media + TapeWritePeriodRatio * RetentionRangeOfFirstDataset.

TapeWritePeriodRatio

It is a global property for the DPM which needs to be set using DPM CLI command. Here is the command to set it
Set-DPMGlobalProperty –DPMServerName <dpm server name> -TapeWritePeriodRatio <fraction>
WritePeriodRatio indicates the number of days for which data can be written on to a tape as a ratio of the retention period of the first data set written to the tape.

WritePeriodRatio value can be between 0.0 to 1.0

Default value is 0.15 (i.e. 15%)




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