On the weekend it came out, being your typical backup geek, I downloaded NetWorker 7.5 SP3, installed a new virtual machine, and started kicking the tyres on the new release. My primary focus was on the AFTD changes. These, as you may recall, compromise some core changes that EMC had previously touted for 7.6 SP1.
I’m quite glad these were pushed down into 7.5 SP3.
The change that was introduced was to give NetWorker a new volume selection algorithm for AFTD devices. Up until 7.5 SP3, NetWorker’s volume selection criteria for AFTD has been:
- If a new backup starts and a device is currently writing (or “writing, idle”):
- If that device’s target sessions have not been met, write to that device.
- If that device’s target sessions has been met, move onto the device that has mounted the least recently labelled volume and start writing there.
- If a new backup starts and no device is currently writing:
- Pick the device whose volume was least recently labelled, and start writing to that.
The net result of this of course is what I like to call the AFTD-data-shuffle. Administrators invariably found that certain disk backup devices within their environment would fill sooner than others, and as a result of this, they’d either continually have to stage from those frequently hit AFTDs to other AFTDs, or stage that data out to tape.
Like the changes announced for 7.6 SP1, 7.5 SP3 now applies a more intelligent volume selection criteria, instead picking the volume that has the least data written to it.
This is, of course, a VGT enhancement – or without the TLA, it’s a Very Good Thing.
There was one minor catch, which prevented me from doing this blog piece. As a result of this change, there was an unanticipated reversal in the volume selection criteria for physical tape – i.e., when there’s no tape with data that is still appendable, NetWorker will pick the most recently labelled tape to write to, rather than the least recently labelled tape to write to.
The good news though is that this is fixed in NetWorker 7.5 SP3 cumulative release 1 (7.5.3.1), which was released last week. So, if you’re after an enhanced volume selection algorithm for AFTD that doesn’t impact physical volume selection, you’ll want to check out 7.5.3.1.