[mythtv-users] TFW, Error: Write() -- IOBOUND ..... and mythbox crashed

George Mari george_mythusers at mari1938.org
Thu Oct 18 11:21:43 UTC 2007

Ma Begaj wrote:
> Hi,
> I had yesterday three recordings running at the same time (1x pvr150,
> 1x pvr500). At the same time, I was watching a recording. And suddenly
> my mythbox crashed and I had to reset it.
> I checked syslog and found nothing, but I found something in
> mythbackend log file:
> 2007-10-17 23:32:05.673 TFW, Error: Write() -- IOBOUND begin cnt(2048) free(835)
> 2007-10-17 23:32:10.724 TFW, Error: Write() -- IOBOUND end
> 2007-10-17 23:32:10.731 TFW, Error: Write() -- IOBOUND begin cnt(2048)
> free(1095)
> 2007-10-17 23:32:10.735 TFW, Error: Write() -- IOBOUND end
> 2007-10-17 23:47:10.183 TFW, Error: Write() -- IOBOUND begin cnt(2048)
> free(1503)
> I checked the older mythbackend logs and I found more of these
> messages in the last few days, usually when I had 2-3 recordings (SD)
> running and watching at the same time.
> I have two IDE hard disks (2x 160GB WD) and 1GB single channel RAM.
> One of these disks has a system and home partitions and a partition
> for myth recordings. 2nd disk is only one partition for recordings.
> Everything is ReiserFS. I was thinking to change it to XFS these days.
> I run "hdparm -tT" and they are more or less the same for both disks:
> root at mythbox:/tmp# hdparm -Tt /dev/hd[ab]
> /dev/hda:
>  Timing cached reads:   1332 MB in  2.00 seconds = 666.17 MB/sec
>  Timing buffered disk reads:  136 MB in  3.03 seconds =  44.81 MB/sec
> /dev/hdb:
>  Timing cached reads:   1090 MB in  2.00 seconds = 545.26 MB/sec
>  Timing buffered disk reads:  172 MB in  3.02 seconds =  56.97 MB/sec
> not pretty fast? this
> http://readlist.com/lists/mythtv.org/mythtv-users/7/39724.html has the
> same problem, and the disks have two or almost three times higher
> "Timing cached reads".
> any ideas? I could buy new disk(s), but I think that these disks
> should be handle 2-3 recordings and 1 reading at the same time.

You may be running into the limit of how many I/O operations per second 
your single disk supports, as opposed to the bandwidth limit.

If you have iostat, (part of the sysstat RPM on my FC6 installation) you 
can run iostat -xk 2 in a shell while you are recording 3 streams and 
watching another to get a picture of your I/O system.  The last column 
gives you % utilization per device, and if it's at or above 100%, well, 
there's your answer.

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