[mythtv-users] Another TFW, Error: Write() -- IOBOUND

George Mari george_mythusers at mari1938.org
Tue Aug 26 13:07:21 UTC 2008


covert covert wrote:
> I am getting the dreaded "TFW, Error: Write() -- IOBOUND" error
> showing in my Mythbackend log. I hope someone can tell me what to
> check next. Done a few test and here are the results..
> 
> While recording 1 x HD stream and 2 x SD streams.
> 
> Output from iostat -xk 2 from just before I got a IOBOUND error to just after.
> 
> -------
> Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s
> avgrq-sz avgqu-sz   await  svctm  %util
> sda               0.00   754.00   16.50   15.00    66.00  3076.00
> 199.49     0.14    4.38   4.00  12.60
> hdb               0.00     0.00    0.00    0.00     0.00     0.00
> 0.00     0.00    0.00   0.00   0.00
> 
> avg-cpu:  %user   %nice %system %iowait  %steal   %idle
>           28.33   15.98    5.08   26.39    0.00   24.21
> 
> Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s
> avgrq-sz avgqu-sz   await  svctm  %util
> sda               0.00   293.00  144.50   25.00   578.00  1272.00
> 21.83     1.29    7.59   5.71  96.80
> hdb               0.00     0.00    0.00    0.00     0.00     0.00
> 0.00     0.00    0.00   0.00   0.00
> 
[deleted]

That line just above - where the %util is 96.80 - tells you everything 
you need to know.  It means your single drive has reached the saturation 
point in terms of IO operations per second.  This is not the same as 
bandwidth, forget about that.  In a nutshell, it means the drive heads 
are already bouncing around as fast as they possibly can, and they're 
being asked to do still more.

Separate your recording drive from your OS drive, at least.  If you've 
already done that, add another drive and use recording groups or RAID to 
distribute the IO load among multiple drives.


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