Re: Read algorithm-raid1/raid10

["Keld Jørn Simonsen" <keld@keldix.com>]

On Tue, Jan 18, 2011 at 12:00:49PM -0200, Roberto Spadim wrote:
> like this patch (a long time ago)
> http://www.spinics.net/lists/raid/msg30003.html
> 
> 
> 2011/1/18 Roberto Spadim <roberto@spadim.com.br>:
> > hi guys, could we implement a load_balance read algorithm for SSD?
> > nearest head isn't as fast as round robin for ssd.
> > i'm talking about raid1 (raid10 too)
> > what's my problem?
> > as i can see, raid0 is faster than raid1
> > for example:
> > two disks raid0 is faster than
> > two disks raid1.
> >
> > why?
> > nearest head
> > instead of a balanced read algorithm (like raid0) the nearest head
> > make raid1 use only one disk for searchs where we could use two disks
> > (like raid0)
> >
> > could we implement a round robin for ssd? and make raid1 as fast as
> > raid0 for ssd?
> > i didn't tested the raid10 algorithm yet.
> > thanks a lot.

This should only be in use for SSDs. For disks it would be a waste of IO
bandwidth. How do we detect whether it is a SSSD.
Another way to accomplish an improvement os to use the offset layout of
raid10.

best regards
Keld