[mythtvnz] Recording dropouts and disk performance...

[Steven Ellis]

On Mon, February 18, 2013 1:30 pm, Stephen Worthington wrote:
> On Sun, 17 Feb 2013 10:10:38 +1300, you wrote:
>
>>On Sat, Feb 16, 2013 at 08:36:45PM +1300, Robin Gilks wrote:
>>> Hi Rob
>>>
>>> You don't say what filesystem you are running or how much free space
>>> you
>>> have available. Also, what space have you asked MythTV to keep
>>> available
>>> as a 'float' so it can record without immediately deleting stuff. Also,
>>> do
>>> you have slow deletes enabled (only useful on some filesystems).
>>>
>>
>>Oops, sorry - the filesystem is ext4. Not sure about the float or slow
>>deletes settings, but I don't remember changing them from the defaults.
>
> Ext4 is not on the recommended list for a recordings partition,
> although quite a lot of people do seem to be using it successfully.
> But you definitely need to check that the slow deletes option is
> switched on with ext4.  The recommended filesystems are JFS and XFS:
>
>   http://www.mythtv.org/docs/mythtv-HOWTO-3.html
>
> I use JFS.
>
> If you are using ext4 with slow deletes off, then whenever you are
> watching a program and finish it and delete it, if you are recording
> at the same time you may have performance problems.  And when your
> drives get full and autoexpire is happening at the same time as a
> recording, then the same problem will happen.
>

Yes make sure slow deletes is turned on.

Also check /proc/mdstat when this happens. There is a chance your raid set
is re-syncing meta-data which will impact performance.

LVM impact is minimal to none these days on modern systems, I seldom build
anything without it.

One other thing to check is hdparm on the raid device, eg

hdparm -tT /dev/md0 /dev/md1

Steve


--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email   - steven at openmedia.co.nz
website - http://www.openmedia.co.nz