elevators and sw raid

[Eric Shubert]

Alan Dayley wrote:
> Maybe http://www.otisworldwide.com/ ?
> 
> (Sorry, couldn't resist.)
> 
> Side track: What does the word "elevator" mean in the context of RAID?
> 
> Alan
> 
> On Tue, Sep 28, 2010 at 8:59 AM, Eric Shubert <ejs at shubes.net 
> <mailto:ejs at shubes.net>> wrote:
> 
>     Is there a particular elevator that generally works best with
>     software raid-1?
> 
>     (More generally, what is the relationship, if any, between elevators
>     and sw raid?)
> 
>     -- 
>     -Eric 'shubes'
> 
>     ---------------------------------------------------

Ha!

In the linux kernel, the I/O scheduler is referred to as the elevator. 
It can be set to one of 4 values in the 2.6 kernel using the elevator= 
kernel parameter at boot time. Each block device's scheduler is 
determined by the value in /sys/block/<device>/queue/scheduler
$ cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]

You can change a device's elevator on the fly by doing:
# echo deadline >/sys/block/sda/queue/scheduler

I'm just wondering which value gives the best performance when using 
software raid-1, or if the choice depends more on the type of load 
that's being processed.

-- 
-Eric 'shubes'