RE: md software raid

["Ian Docherty" <idiandocherty@googlemail.com>]

> -----Original Message-----
> From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
> owner@vger.kernel.org] On Behalf Of Robin Hill
> Sent: 23 October 2009 10:38
> To: linux-raid@vger.kernel.org
> Subject: Re: md software raid
> 
> On Fri Oct 23, 2009 at 02:11:09AM -0700, ian.d wrote:
> 
> >
> > hello
> >
> > As a newbie to Linux kernel etc.
> >
> > How do you tell which version of md software raid is included in a
> > specific kernel version?
> > Is there a command to run which will return this info?
> > Is it possible to install different versions of md in different
> kernels?
> >
> There's two separate components to Linux software RAID - the md code in
> the kernel, and the mdadm application which interfaces with it.  I very
> much doubt the kernel code is versioned at all, other than by the
> kernel version (or GIT version).  The mdadm application is versioned,
> and you can get the installed version by running 'mdadm -V'.
> 
> Some of the mdadm functionality will only work with newer kernel
> versions, but you should be able to run any version with any kernel
> (within reason anyway) and make use of the core functionality.  There
> may be some exceptions here, but they should be detailed in the release
> notes for specific versions.
> 
> As for changing the md version in the kernel - it may be possible, but
> generally there's a lot of work involved in back/forward porting code
> between kernel versions (because of changes to core structures, etc).
> 
> Is there any particular reason you're asking this (e.g. needing to use
> some of the latest functionality with an older kernel)?  You may get a
> more definitive answer if you have a specific case.

Thanks this info was very helpful.

The reason I asked was because I have been following a thread re MD-XFS 50%
write performance issue with different kernel releases and as performance is
important to me  I was thinking it might be better for me to use an older
kernel (2.6.28.4) but keeping md,mdadm functionality up to date 

Ian.d


> 
> HTH,
>     Robin
> --
>      ___
>     ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
>    / / )      | Little Jim says ....                            |
>   // !!       |      "He fallen in de water !!"                 |