quoted

quoted

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