[mythtvnz] Recording dropouts and disk performance...

[Robin Gilks]

>
> Hi All,
>
> Over the past couple of weeks I've had a few recordings drop out after
> several minutes. Today I finally got around to looking in the log files
> for one of the affected recordings:
>
> 2013-02-14 21:38:59.782815 E [1609/24862] DVBRead
> ThreadedFileWriter.cpp:217 (Write) -
> TFW(/mnt/recordings/1001_20130214083000.mpg:110): Maximum buffer size
> exceeded.
>                         file will be truncated, no further writing will be
> done.
>                         This generally indicates your disk performance
>                         is insufficient to deal with the number of
> on-going
>                         recordings, or you have a disk failure.
>
> My disk setup is 2x2TB drives set up using software RAID 1 and LVM, with
> the system and database partitions being hosted on the same drives as
> the recordings. This setup has worked fine until recently - I did have
> one drive die a while back, but I returned it under warranty.
>
> I've looked in the system logs and SMART data and don't see anything
> to indicate that a drive is failing, so I'm confused as to why this
> has only started recently as nothing has changed in my setup.
>
> There seem to be several other people around the internets having
> similar issues, but no solutions are proposed.
>
> Has anyone else here had a similar issue? Or does anyone have any tips
> for tuning/cleaning up that my help the disk performance?
>
> Thanks in advance,
>
> Cheers,
>
> Rob

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).

I do find it odd that a Raid 1 system is so slow - my Raid 5 system, which
in theory is 1/4 the speed (at best!) handles 8 simultaneous recording OK
with a mixture of DVB-T, DVB-S and analog off a set=top box.

Might be worth playing this tune:
http://systembash.com/content/simple-disk-benchmarking-in-linux-using-dd/
just to actually measure a single file write. Shouldn't be too difficult
to run the same in 2 terminals to test the 2 files scenario.

Cheers

-- 
Robin Gilks