[ale] Fwd: Re: [ale] Recommendations on mirrored LVM..?

[James P. Kinney III]

I think from a logical (no pun intended) standpoint, LVM on the raw
disks and raid on top makes more sense to me. LVM constructs a virtual
partition which raidtools then uses for drive space. 

Mirrors can be worked "on the fly" but with degraded performance in some
forms. If a mirror is broken, stuff added or changed on one partition,
then the mirror is reassembled, performance will be lower while the
mirror re-syncs.

In your example setup you asked if you can add a second LV to an
existing raid configuration. No. That would be a new raid configuration.
Can you extend/grow an existing raid configuration by adding more space
to the LV's that comprise the raid volumes? Yes. This is what LVM is
good for. Break the mirror, resize the md's, reform the mirror, allow
time for re-sync (should be short if no changes occurred).

Now for the $40,000 question. Can all this be done on a live production
system with data being written to and read from mirrored drives? I don't
know yet. From the reading I've done, it appears that it is possible. I
am not currently running LVM on my systems. I have been watching the
enterprise development and the ability to do this on the fly has always
been a goal. Extending a logical volume is probably OK live. Shrinking
is probably not. That requires an fsck which requires an unmounted
partition.

Hard stuff.

On Sat, 2002-06-15 at 11:41, Eric Webb wrote:

> Ahh, so you think it's better to go put LVM on the raw disks and then put
> raidtools on top of that..?
> 
> Here's the question, though:  With Linux, can you make and break mirrors on
> the fly?  Let's say I start with one drive now and add a second PV to the LVM
> configuration.  Once I've done that, can I add a second LV to the RAID 1 that
> I created earlier?  Or do I have to start from freakin' scratch?
> 
> (If the answer is Yes (start from scratch), then I wonder how the hell
> these guys claim Linux is now at the enterprise level?! )
> 
> -E.
> 
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GPG ID: 829C6CA7 James P. Kinney III (M.S. Physics)
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