Re: Advice on raid/lvm
On Thu, Apr 09, 2009 at 10:00:40AM +0300, Tapani Tarvainen wrote:
> On Wed, Apr 08, 2009 at 06:02:26PM -0300, Henrique de Moraes Holschuh (hmh@debian.org) wrote:
> > On Wed, 08 Apr 2009, Miles Fidelman wrote:
> > I suggest that a small (1GB-4GB) partition for simple md-raid1 be used for
> > / instead. That won't give you any headaches, including on disaster
> > recovery scenarios.
If you're going to have separate partitions (e.g. /usr, /var, /home),
then I would not call a 1-4 GB / "small". I have a 500 MB / of which
only 117 MB is used.
> I would respectfully disagree. There are significant advantages in
> putting / in LVM, it is a well-supported, standard configuration,
> and avoiding it only gives false sense of security: in a disaster
> situation you need to know basics of mdadm and lvm anyway, if
> you use them.
> Yes, leaving / out of LVM does give you a more complete
> environment to work with when system crashes in a way that LVM
> (the volume group containing /) is inaccessible.
> It doesn't help much though unless you also leave /usr out,
> and I've lost count on how often I've enlarged /usr and
> been grateful it was under LVM.
What is in /usr that you'd need (ok, other than man pages)?
> All the essential tools for managing software raid and lvm are,
> however, available even without / - indeed they're in initrd,
> and if you can't use them, you're out of luck anyway.
You don't have whatever notes you've left yourself in /root
> On the other hand, having / in LVM means:
> * you can enlarge / when necessary;
You should never have to enlarge a 500 MB /
> * you can encrypt / if desired;
Why would you need / encrypted (if swap, /tmp, /home, and parts of /var
are encrypted)?
> * you can use other RAID configurations besides RAID1 with /;
True, but for 500 MB is that helpful? If you have more than 2 disks,
just put a 500 MB partition on each and have more than 2 components to
the raid1 array.
> * you don't have to create separate volumes for each of
> /usr, /var and /tmp (although you probably should anyway);
> * it's the standard configuration, offered as automatic default
> installation option, and many people are using it so finding
> someone to help when needed shouldn't be hard.
I've never used the automatic default; It always wastes resources on my
boxes.
> As for the rest of your points, well, both software raid
> and lvm do increase complexity and require learning some
> new tricks, but they're well worth the trouble if you
> manage any system more complex than a simple workstation,
> IMHO.
Figure out what all documentation, man pages (in text format), notes,
etc that you would want and put them in /root/doc. Any scripts that you
find helpful for rebuilding arrays you could put in /root/bin.
Doug.
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