Re: RAID extremely slow

[Kevin Ross]

On 07/25/2012 10:00 PM, Kevin Ross wrote:
> > > > unused devices:<none>
> > > >
> > > > # cat /proc/sys/dev/raid/speed_limit_min
> > > > 10000
> > > MD is unable to reach its minimum rebuild rate while other system
> > > activity is ongoing.  You might want to lower this number to see if 
> > > that
> > > gets you out of the stalls.
> > >
> > > Or temporarily shut down mythtv.
> >
> > I will try lowering those numbers next time this happens, which will 
> > probably be within the next day or two.  That's about how often this 
> > happens.
>
> Unfortunately, it has happened again, with speeds at near zero.
>
> # cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md0 : active raid6 sdh1[0] sdd1[9] sde1[10] sdb1[6] sdi1[7] sdc1[4] 
> sdf1[3] sdg1[8] sdj1[1]
>       6837311488 blocks super 1.2 level 6, 512k chunk, algorithm 2 
> [9/9] [UUUUUUUUU]
>       [=>...................]  resync =  8.3% (81251712/976758784) 
> finish=1057826.4min speed=14K/sec
>
> unused devices: <none>
>
> atop doesn't show ANY activity on the raid device or the individual 
> drives.
> http://img687.imageshack.us/img687/2913/screenshotfrom201207252.png
>
> Also, I tried writing to a test file with the following command, and 
> it hangs.  I let it go for about 30 minutes, with no change.
>
> # dd if=/dev/zero of=test bs=1M count=1
>
> dmesg only reports hung tasks.  It doesn't report any other problems.  
> Here's my dmesg output:
> http://pastebin.ca/2174778
>
> I'm going to try rebooting into single user mode, and see if the 
> rebuild succeeds without stalling.
>
> -- Kevin

It rebuilt fine in single user mode, with speeds usually around 
50MB/sec.  But after exiting single user mode, and allowing MythTV and 
other programs to start, within 30 minutes I had the problem again.  
Basically a hung filesystem.  I couldn't even "cat /proc/mdstat", that 
just hung.  Lots of hung task warnings in dmesg.

Because Phil suggested that fsync calls might cause stalls, I commented 
out the fsync in MythTV.  I'll run with that for awhile, and see how 
things work out.  So far it isn't adversely affecting MythTV.

Thanks!
-- Kevin

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