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Re: [linux-lvm] software RAID over LVM



Austin,

Just as an aside, I have done all of those configurations with no LVM involved. RAID0+1, RAID1+0, and RAID5 on top of mirrored devices. Yes RAID1+0 isn't very smart, but we did it. It is much simpiler, and more reliable to have RAID underneath LVM. Not because LVM is unreliable, but if you forget, or don't realize both halves of a mirror got migrated to the same disks your mirror might be a lot less redundant then you believe it is. Wow, I just restated the a FAQ entry in a very poor manner...

LVM didn't try to be all incompassing. It could have been, but it would have made things more complicated and duplicated a bunch of work from what I have read on this list.

Kirby


Austin Gonyou wrote:
I can think of MANY uses for this. The main one would be a relatively
cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
any hardware to do this with, then software is next. It'd be nice to be
able to do this, for sure. You could even do 0+5, or something crazy
like that too.


On Tue, 2002-01-29 at 17:50, Kirby C. Bohling wrote:


Paul,

I haven't done it. I have done mirrors underneath, but I am
curious what is the reasoning and/or application. The only thing I can think up is so you can migrate your mirrors to faster drives easily. However, putting the mirror underneath should allow you to move off one mirror onto another.


I don't believe that mirroring can be expanded like a filesystem
can. In order to make the mirror bigger, you have to break the mirror as far as I know. So what are you planning on doing with it, or is it just "to see if it could be done".


	Thanks,
		Kirby

lvm agilecat mailshell com wrote:

Hi all,

I understand the use of LVM over software RAID.
But is it possible to use software RAID ON TOP
of LVM?  For example, have a RAID-1 mirroring
array created from two logical volumes.

I've tried and it seems to be working.  Is
it safe to do this?  Any pitfalls?

Thanks!

Paul

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