Dell PowerVault DR6000 - Manual (Page 8)

8 Setting up NetVault Backup Native Virtual Tape Library on the Dell™ DR4X00 Disk Backup Appliance
and to set the drive count to equal the number of simultaneous jobs or data streams desired without
exceeding the maximum guidelines set forth by the vendor.
For Example: Starting with a storage appliance with 2TB of physical disk space. Based on the 10x usage
recommendation, one can create a VTL of 20TB of total storage. But given that the data backed up per
week is 2TB and data retention is 4 weeks, the total amount of data stored at any given time would only be
8TB. Cutting the VTL down to 10TB would then be a more efficient use of space.
Once the overall size of the VTL is determined, the number of virtual drives to create and the granularity of
the VTL is the next consideration.
Most storage appliance operating environments can effectively handle a set number of streams. Any read
or write operation to and from a VTL virtual drive would denote a stream. As a rule of thumb, the number
of virtual drives to create in the VTL should reflect what is required to support simultaneous streams, or
concurrent jobs. Creating an excessive number of drives does not yield any benefits and could lead to
performance degradation. It is important to also never exceed the number of streams supported by the
appliance vendor’s operating environment when creating VTLs and virtual drives.
Media size is the final consideration when creating a VTL. Unlike physical media, virtual media can be
created to any size within the allowed range set by the appliance. So proper media size selection is
important to ensure smooth operation of the VTL. Creating a small number of large media will extend the
retention of expired data and prevent proper recycling within a media pool. Creating a large number of
small media puts a strain on the NVBU Media Manager process and can cause contention of resources. We
recommend that the media size be made to accommodate for the media group retention policy such that
when the retention period is expired for that group all items on the media should expire as well thus
allowing for the reuse of the virtual media in question.