Re: [MLUG] software raid conifg - fedora

[Mark Haidekker <EMAIL:PROTECTED>]

On Thu November 10 2005 17:07, Dave Lloyd wrote:
> On Thu, 10 Nov 2005, Shawn Parker wrote:
> > when configuring a software raid in fedora core 4, how do you set up
> > an "extra" disk for raid1? i have 3 80GB drives in my server. i would
> > like to set up a raid1 (mirror) of 2 drives and use the 3rd as an
> > extra drive incase one fails?

Yes, this is the strategy. You can set up one drive as "spare" that can be hot 
added if another drive fails. 

> > how does one do this? do i configure the raid1 using all 3 drives and
> > simply set the "extra drive" parameter to 1? do i clone hda to hdc and
> > hdd so that each drive is *exactly* the same, first?

The third drive should match the first two.

> > i have no problem setting up a standard raid1 with just 2 drives...but
> > i'm a little confused when using a 3rd for an extra in fedora's
> > partition manager.
>
> Not that I have an answer, but I've got a question:  why do you want to
> do this?  It's my experience that the second drive will not fail until
> you can replace the first failed drive unless:
>
> 1) There's a hardware problem where drives of a certain age fail
>    (mechanical, de-soldering of chips, etc.).
> 2) Outside environmental influences.

I would agree with that. If one drive fails, you'll realize the problem real 
quick. There is still enough time to replace the drive before the second 
drive also fails. I had that situation recently - the intact drive is still 
intact. Furthermore, after drive replacement, no data was lost.

> My personal opinion, and my experience backs me up here, is that
> operator error that causes data loss is FAR more likely than a disk
> failure.  You're better off doing a weekly backup to your third disk and
> sticking it in a file drawer than having a hot spare that can come in
> and replace a failed volume.

As I mentioned above, disk failures do occur, and I had a RAID case recently. 
I was glad I had RAID set up on that server, but I did not miss the spare 
drive.

IMO, if you have 3 drives, configure them as RAID5. You'll get 160 MB, 66% 
efficiency instead of 50%.

> Oh, and please, please do not mirror swap.  Mirroring really cuts write
> performance, and if you start to write to swap, well, things will begin
> to suck much more than a "normal" condition under which you write to
> swap.

Right - but having one swap partition on each drive is great. Actually, some 
people recommend RAID0 for swap to speed it up.

Mark

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