[clue-tech] RAID5

[Luke Wahlmeier]

Well I have heard this question alot.  In general raid 5 is static,
you can not resize it, once you make the array you are stuck with an
(base) array that size.  If one drive fails obviously you can run with
out it, I mean thats what raid 5 is for, but you will be in "degraded"
mode, meaning that if another drive fails, you lose you array, and
possibly all data on it.

There is one tool that does some tricks to allow you to resize a linux
software array.  It is very dangerous and should only be used if you
know what you are doing and have a very resent back up
http://unthought.net/raidreconf/

Remember there is more to consider here then just resizing the array,
it more then likely has a files system on it that will have to be
resized to a size that will fit on the new array.

4x18 = 54gb on a raid 5
if you want to keep redundancy on it and remove a drive you total
space is going to drop by a drive.
3x18 = 36gb

If you use the resize tool reduce the size of the filesystem to <36gb
first, or you will loose everything.

Honestly it would probably be easier to copy everything to another
drive, destory and remake the array, if thats an option.



On 12/13/06, Kevin Fenzi <kevin at scrye.com> wrote:
> On Wed, 13 Dec 2006 00:17:37 -0700
> wt at penguintechs.org (Warren Turkal) wrote:
>
> > On Tuesday 12 December 2006 12:18, David L. Willson wrote:
> > > I'd like to do everything hot, if I can.  Does anyone have advice
> > > before I begin?
>
> Linux software raid? Recent distro?
> If so, then it should be pretty simple:
>
> mdadmin /dev/md0 --remove /dev/whateverdeaddrive
> <shutdown and pull drive, put replacement drive in>
> mdadmin /dev/md0 --add /dev/replacementdrive
>
> (where md0 is your raid device...)
>
> If you are using a hardware raid, see your bios raid management thing
> or the like.
>
> >
> > I don't believe that RAID5s can be resized while hot in Linux.
>
> Not true. You can indeed do so since 2.6.17...
>
> See: http://scotgate.org/?p=107
>
> for example.
> >
> > wt
>
> kevin
>
>
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