[mythtv-users] Backend crash. Do I have too few hard drives?

Paul Gardiner lists at glidos.net
Sat Dec 4 12:14:30 UTC 2010

On 04/12/2010 11:30, Mike Perkins wrote:
> Paul Gardiner wrote:
>> I've been running MythTv for several years with no real problems.
>> Particularly the backend has been very reliable. Recently I added
>> a Nova S2-HD card to the backend so that I could pick up Freesat.
>> I also added a second HDD, so that I have one for system and one
>> for recordings. I paritioned the recordings disc into two partitions.
>> Can't remember why I did that. Perhaps that's making things worse.
>> Anyway, since the addition, the backend has been on occasion
>> unreliable. Tonight
>> was an example. I had one HD recording on the go, which I was
>> simultaneously watching. That was fine, until two SD recordings started
>> up. That caused the backend to die. I had an empty log file, which
>> happens sometimes. I'll try to get more information next time
>> it happens.
>> Could this be lack of HDD bandwidth?
>> Oh yeah, since the addition, I've upgraded from 0.23.1 to 0.24.
>> That seemed to make the backend more reliable, until tonights
>> crash. A week ago, I rebuilt the backend from the then latest
>> 0.24 fixes, so I'm pretty much up to date.
> Not sure about your crashes, but I doubt that splitting your hard disk
> into two partitions is going to help. While you're making one recording,
> the head is going to be reasonably static over the part of the disk it's
> writing to. Once you start up another simultaneous recording the head is
> going to be thrashing about. Two (or more) partitions guarantees that
> the head is going to have to move a considerable distance each time. Not
> good. Head movement = seek time = delay.
> Now modern disks can probably cope with most of this but why make the
> situation worse when it's not necessary? As a rule of thumb I try to
> arrange one disk (= partition) per tuner. That way, although sometimes
> the storage allocation chooses the same directory, you at least stand a
> chance that each recording will write to a separate disk and the heads
> won't be moving too much.
> (Now the fact that all these will be writing to separate seek tables in
> the database, that's another story. Just hope that mysql does the right
> thing.)

Yes, my thoughts exactly. I still have no idea why I partitioned it.
Although thinking about it again now, for two simultaneous recordings
to the two partitions, it might avoid them getting fragmented, which
would help on playback. I doubt it though. Sounds like it wasn't
a great idea.

Anyway, looks like my problems aren't connected with that. I just tried
for experiment repeating the conditions of the crash. This time no
problems, and I then made it more difficult by watching another HD
channel live. So I was recording 2 SD channels, 2 HD channels, and
playing back 1 of the HD channels. Still no problem.

I guess I'll have to wait for the problem to occur again, and hope
I have logs.


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