Q: /sys/block and I/O Schedulers

[Ulrich Windl]

Hi!

I have a question: Reading the docs on I/O Schedulers, I had the impression the docs wanted to tell me that only the low-level devices (i.e. disks) use I/O Schedulers, while higher-level devices (like multipaths, RAIDs, LVs, etc.) don't.

Using the SLES11 SP1 kernel (2.6.32.43-0.4-xen), I found out that LVs seem to use the I/O Scheduler, while RAID1 don't seem to do so. Also a disk in a Xen DomU also uses an I/O Scheduler (in addition to those being used in Dom0 for the same device already)

Is that correct, and if so, why is that? Is there a change to be seen in the future?

My test was as simple as this:
/sys/block # for d in *
> do
> echo $d: $(<$d/queue/scheduler)
> done
cciss!c0d0: noop anticipatory deadline [cfq]
dm-0: noop anticipatory deadline [cfq]
[...]
loop0: none
[...]
md4: none
sda: noop anticipatory deadline [cfq]
[...]

As I'm not subscribed to the list, I'd appreciate any CC: to my address. Thanks!

Regards,
Ulrich


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