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Tiny Deathstars of Foulness

I see a numer of environments that are running routine defragmentation scripts on Xsan volumes. I do not agree with this practice, but given certain edge cases I have watched it happen. When defragmenting a volume, there is no reason to do so to the entire volume. Especially if much of the content is static and not changing very often. And if specific files doesn’t have a lot of extents then they are easily skipped. Let’s look at a couple of quick ways to narrow down your defrag using snfsdefrag. The first is by specifying the path. In this case you would specify a -r option and follow that with the path starting path you want to recursively seek fragmented files. The second is to limit the number of extents in the file. To combine these, let’s assume that we are looking to defragment a folder called Seldon on an Xsan volume called Harry. snfsdefrag -r -m 25 /Volumes/Harry/Seldon You should also build logic into scripts if you are automating the events. For example, you could also use the -c option to just look at how many extents there are and perform the actual defragmentation as part of an if/then only in the event that there are more than a specified threshold. Another example is to check that there isn’t an existing process running in snfsdefrag. Also, if there is then don’t fire up yet another instance:
currentPID=$(ps -ewo pid,user,command | grep snfsdefrag | grep -v grep | cut -d ” ” -f 1) echo The current snfsdefrag PID is ${currentPID} so we are aborting the process. > $logfile
If you insist on automating the defragmentation of an Xsan volume, then there’s lots of other little sanity checks that you can do as well. Oh, you’re backing up, right?

February 13th, 2010

Posted In: Xsan

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The snfsdefrag tool is used for Xsan defragmentation.  It can be run on a volume by using the following command: snfsdefrag -r <VolumeName>

April 9th, 2008

Posted In: Xsan

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Xsan volumes can get fragmented.  This can cause the performance to move to a grinding halt.  Dropped frames, slow copy times, even volume corruption are common side effects.  So, to defrag the volume you can use snfsdefrag.  This command-line tool will defrag volumes or files.  You can even specify what to do with the fragmented data, giving you a way to move data between storage pools…

March 9th, 2006

Posted In: Xsan

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