With this feature, you can achieve better tape utilization by co-locating data from multiple protection groups with similar retention range. This feature is disabled by default. You can use following PowerShell commands to enable and disable tape co-location.
Enable Tape co-location:
Set-DPMGlobalProperty -DpmServer <DPM Server Name> -OptimizeTapeUsage $true
After data co-location has been enabled, DPM will check for the following conditions before allocating a tape:
- 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) * TapeExpiryTolerance
Lower Bound: furthest expiry date among all the datasets on the tape + (furthest expiry date among all the datasets on the tape – current date) * TapeExpiryTolerance. - Current time should be less than first backup time of the dataset on the media + TapeWritePeriodRatio * RetentionRangeOfFirstDataset.
A dataset will be collocated only if both the above conditions are true.
When you add the value to the registry, set the DWORD to be the actual percentage in decimal. The Default is 17 percent if that value is not present. Most likely you need to increase that value to a higher percentage and in some cases you need to set it to 100 in order for tape co-location to work as desired.
TapeWritePeriodRatio – Indicates the number of days for which data can be written on to a tape as a fraction between 0 and 1. The default value is 0.15 – meaning by default, we will write to the same tape for 15% of the retension range period specified for each PG.
TapeWritePeriodRatio is not a registry. 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>
EXAMPLE, to set the write period ratio to 50%, use the following command.
Set-DPMGlobalProperty –DPMServerName MY-DPMSEREVR -TapeWritePeriodRatio .50