Weird blocks at fsync() calls using md

[Sander Smeenk <ssmeenk@freshdot.net>]

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Hello list,

I've recently subscribed to this list as i'm facing a little problem
using md v0.90.3 (bitmap v4.39) on Linux 2.6.17.1, Debian 'sid', mdadm
2.4.1...

While the system is under heavy disk IO, calls to fsync() made by vim
(for example) block for a LONG time. Like 30 seconds or more. I'm not
sure if it also blocks other IO during that fsync() wait, but it's nasty
enough to have your :w action take 30+ secs...

My system is running in RAID1 on two SCSI U320 disks:
Personalities : [raid1] 
md0 : active raid1 sdb[0] sdc[1]
      71819392 blocks [2/2] [UU]

Some guy on IRC told me he had the same problem once, and it was related
to some whacky locking mechanism used in the software raid code? I'd
really like to know if this is a common problem and what i can do about
it.

Any ideas are welcomed!

Thanks alot,
Sander Smeenk.
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