Re: wish for Linux MD mirrored raid types

From: "Keld Jørn Simonsen" <keld@keldix.com>
To: Jonathan Tripathy <jonnyt@abpni.co.uk>
Cc: "Keld Jørn Simonsen" <keld@keldix.com>,
	"Roman Mamedov" <rm@romanrm.ru>,
	linux-raid@vger.kernel.org
Subject: Re: wish for Linux MD mirrored raid types
Date: Fri, 6 May 2011 11:41:02 +0200	[thread overview]
Message-ID: <20110506094102.GC22245@www2.open-std.org> (raw)
In-Reply-To: <4DC3BDD9.1060300@abpni.co.uk>

On Fri, May 06, 2011 at 10:22:33AM +0100, Jonathan Tripathy wrote:
> 
> On 06/05/2011 10:03, Keld Jørn Simonsen wrote:
> >On Fri, May 06, 2011 at 01:31:59PM +0600, Roman Mamedov wrote:
> >   
> >>On Fri, 6 May 2011 09:17:52 +0200
> >>Keld Jørn Simonsen<keld@keldix.com>  wrote:
> >>
> >>     
> >>>I would like linux MD raid10 functionality to be part of the Linux MD
> >>>RAID1 module, and be called raid1. This is in accordance with the
> >>>use of the RAID1 term as standadized by SNIA. In fact the RAID10-offset
> >>>layout is an implementation of a SNIA RAID specification. The RAID10-near
> >>>layout is an implementation of a simple RAID layout. And the RAID10-far
> >>>layout is just another layout far a mirrored RAID.  So all these types
> >>>could just be defined as different RAID1 layouts.
> >>>       
> >>RAID1 is RAID1, RAID10 is RAID10.
> >>RAID1 on 4 drives is very different from RAID10 on 4 drives.
> >>Don't add confusion by trying to rename RAID10 to RAID1.
> >>     
> >How are they different?
> >Say what is the difference between a Linux MD RAID1 with 4 disks, and
> >the default Linux MD RAID10 with 4 disks? (in the near layout)?
> >
> >   
> RAID1 is traditionally a mirror only setup (ok, some RAID 
> implementations may do some load-balancing of some sort). So a RAID1 
> with 4 disks is one data set copied onto 4 disks. Bandwidth is roughly 
> the same as a single disk (ignoring any load balancing).
> RAID10 is mirror and stripe. A RAID10 with 4 disks is similar to a 2 
> disk RAID0 (double bandwidth with data split in half across both disks), 
> but with each disk having a mirror (which brings the total up to 4 drives).
> 
> Additionally, a RAID1 disk (at least using MD) can be accessed just like 
> a normal disk (good for recovery etc.) however a single disk out of a 
> RAID10 array is next to useless.

I think you are demonstrating some of my points about general knowledge
quite nicely. Don't worry, you are not alone.

best regards
keld
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html