Antw: Q: /sys/block and I/O Schedulers

Antw: Q: /sys/block and I/O Schedulers

[Ulrich Windl]

>>> Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de> schrieb am 22.08.2011 um 12:10
in Nachricht <4E522B1A.1E1 : 161 : 60728>:
> 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 

Forget the statement about RAID1; I just overlooked it in the list.

> 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
> 
>