Thomas Jager wrote:
Hi list.
I run a file server on MD raid-5.
If a client reads one big file and at the same time another client
tries to write a file, the thread writing just sits in uninterruptible
sleep until the reader has finished. Only very small amount of writes
get trough while the reader is still working.
I'm having some trouble pinpointing the problem.
It's not consistent either sometimes it works as expected both the
reader and writer gets some transactions. On huge reads I've seen the
writer blocked for 30-40 minutes without any significant writes
happening (Maybe a few megabytes, of several gigs waiting). It happens
with NFS, SMB and FTP, and local with dd. And seems to be connected to
raid-5. This does not happen on block devices without raid-5. I'm also
wondering if it can have anything to do with loop-aes? I use loop-aes
on top of the md, but then again i have not observed this problem on
loop-devices with disk backend. I do know that loop-aes degrades
performance but i didn't think it would do something like this?
I've seen this problem in 2.6.16-2.6.21
All disks in the array is connected to a controller with a SiI 3114 chip.
I just noticed something else. A couple of slow readers where running on
my raid-5 array. Then i started a copy from another local disk to the
array. Then i got the extremely long wait. I noticed something in iostat:
avg-cpu: %user %nice %system %iowait %steal %idle
3.90 0.00 48.05 31.93 0.00 16.12
Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
....
sdg 0.80 25.55 0.00 128 0
sdh 154.89 632.34 0.00 3168 0
sdi 0.20 12.77 0.00 64 0
sdj 0.40 25.55 0.00 128 0
sdk 0.40 25.55 0.00 128 0
sdl 0.80 25.55 0.00 128 0
sdm 0.80 25.55 0.00 128 0
sdn 0.60 23.95 0.00 120 0
md0 199.20 796.81 0.00 3992 0
All disks are member of the same raid array (md0). One of the disks has
a ton of transactions compared to the other disks. Read operations as
far as i can tell. Why? May be connected with my problem?
-
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
