Comment 796 for bug 500069

I'm still seeing this.

Setup: Debian 7 Wheezy, amd64 backports kernel (3.11-0.bpo.2-amd64), ~45MB/s write of a low number of large files by rsync (fed through a GBit ethernet link) on an ext3 FS (rw,noatime,data=ordered) in a LVM2 partition on a hardware RAID5.

Observation: The machine (32-core Xeon E5-4650, 192 GB RAM), primarily servicing multiple interactive users via SSH, x2go and SunRay sessions, gets completely unusable during and quite some time after the rsync transfer. TCP connections to SunRay clients time out, IRC connections are dropped, even simple tools like "htop" don't do anything but clear the screen after being started. "iotop" shows a [jbd2/dm-1-8] process on top, reportedly doing "99.99%" I/O (but not reading or writing a single byte, maybe because it's a kernel thread?).

Once I switch from the default CFQ I/O scheduler to "deadline" (echo deadline > /sys/block/sdb/queue/scheduler), the symptoms disappear completely.