[linux-lvm] Misleading documentation (was: HDD Failure)
fabien at jakimowicz.com
Wed Sep 20 00:35:41 UTC 2006
On Tue, 2006-09-19 at 15:40 -0700, Scott Lamb wrote:
> On Sep 18, 2006, at 12:37 PM, Mark Krenz wrote:
> > LVM != RAID
> > You should have been doing RAID if you wanted to be able to
> > handle the
> > failure of one drive.
> This is my biggest beef with LVM - why doesn't *any* of the
> documentation point this out? There are very few good reasons to use
> LVM without RAID, and "ignorance" certainly isn't among them. I don't
> see any mention of RAID or disk failures in the manual pages or in
> the HOWTO.
> For example, the recipes chapter  of the HOWTO shows a non-trivial
> setup with four volume groups split across seven physical drives.
> There's no mention of RAID. This is a ridiculously bad idea - if
> *any* of those seven drives are lost, at least one volume group will
> fail. In some cases, more than one. This document should be showing
> best practices, and it's instead showing how to throw away your data.
> The "lvcreate" manual page is pretty bad, too. It mentions the
> ability to tune stripe size, which on casual read, might suggest that
> it uses real RAID. Instead, I think this is just RAID-0.
>  - http://tldp.org/HOWTO/LVM-HOWTO/recipeadddisk.html
LVM is just a Logical Volume Manager. It sounds like it add a layer
between physical devices and logical volumes. A such layer can take care
of physical devices failure, but lvm does not. Maybe you are right and
it should be pointed out. Maybe not ...
Having a half block device make no sense because there are actually no
filesystem capable of recovering this kind of failure.
Fabien Jakimowicz <fabien at jakimowicz.com>
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