[mythtv-users] Storage Groups, free space, (and auto-expire?)

[Ryan Steffes]

On 10/24/07, Brian Guilfoos <mythtv at guilfoos.com> wrote:
> [Sorry for the dissertation-like length.  Being surrounded by PhDs at
> work must make me more verbose.]
>
> I have what I imagine is a common situation - I've upgraded to SVN to
> get Storage Groups, and I have drives of wildly varying capacities
> (100GB, 500GB, and 1500GB).  To make matters slightly more concerning,
> the drive local to the master backend (and thus used most heavily in
> recording) happens to be the smallest drive, which should then fill up
> quickly.
>
> Curious as to how that would effect drive usage and auto-expire, I
> decided to look at the code (since the answer wasn't in the archives),
> and I learned a few things about how a drive is selected for a
> recording.  I wanted to document this here for other users, and because
> I believe there is a potential performance issue in situations similar
> to mine.
>
> As documented on the Wiki (
> http://www.mythtv.org/wiki/index.php/Storage_Groups_Weighting ), there
> is a weighting algorithm in Scheduler::FillRecordingDir() that
> calculates which drive is optimal performance wise to record to.  What
> isn't documented there is how free space on the drive is taken into
> account.  The scheduler will attempt to place the recording on the
> "best" drive according to the weighting algorithm that has enough
> estimated space for the recording based on the recording length and the
> maximum bitrate for that tuner.  If there is no drive with enough space,
> then the "best" drive is chosen regardless, and something will have to
> be auto-expired from that drive to make space - *** which is not
> necessarily the oldest or lowest priority recording *** !
>
> Now, I believe this is pretty much the best way of choosing where to
> store the recording.  Perhaps the "all drives are out of space"
> condition might choose a drive based on what would be expired, but that
> starts to get complicated - and really isn't the aim of this post.
>
> My concern is that the local drive - my smallest - will fill rapidly and
> then be effectively "removed" from the storage group for recording
> purposes.  It seems that a utility to balance free space in storage
> groups might be useful - something to move older recordings from a
> fuller filesystem to one with more space - to allow the scheduler to use
> all available drives in a Storage Group.
>
> Thoughts?  Does anyone else see a potential utility in something like
> this?  I've got enough storage space that the auto-expire problem is a
> long way off (and thus not a major concern).  But keeping the local
> drive available for recordings /is/ a concern of mine, so I'm willing to
> work on a general-purpose solution if other people could utilize my work.


The "easiest" way is a simple script run at regular intervals that
checks mythshutdown to see if things are idle, then checks disk space
to see if something is getting full, then proceeds to move files from
the smaller drive to the larger drive.  If they are in the same
storage group, which drive they are on doesn't matter much.

I used to have a script similar to that, but I seem to have lost it
the last time I mucked everything up and had to reformat and
reinstall.

Ry