Hi all!

I have 2 DRBD clusters - one cluster with Pentium 4 3.2 GHz CPUs and
"3ware 7000-series ATA-RAID" controllers with RAID1 over two 75GB SCSI
disks each, the other with Xeon 3.2 GHz CPUs and "Adaptec SmartRAID V"
controllers with 6 disks (RAID0 over 3 RAID0), both with a
2.6.15-1-em64t-p4-smp kernel kernel from Debian/Sarge backports
(admittedly from many months ago).
Typical workload is manipulating many many small files. However the
nightly backup job (especially on the 6-disk hosts) job stresses the I/O
subsystem that much that it blocks the rest of the host almost
completely unusable and programs run into timeouts on I/O.
That kernel uses per default the "anticipatory" I/O scheduler (which
seems to be the problem of the starvation).
I wonder
- if there is any risk involved in changing that (via kernel command
  line and/or via /sys/block/<devicename>/queue/scheduler) to "cfq" -
  the presumbly best one, and
- if that interferes with DRBD on top, and
- if that actually buys anything, especially avoids the starvation.

Thanks in advance,
	Bernd
-- 
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