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

[James P. Kinney III]

On Sun, 2002-06-16 at 00:08, Eric Webb wrote:
> On Saturday 15 June 2002 01:26 pm, James P. Kinney III wrote:
> >
> > 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.
> 
> Well, what I really meant was to start off with no raiding and then add in a 
> mirror later.  I think you've already answered that question though.

Yes, a mirror can be added later without blanking the hard drive with
the original data. 
> 
> > 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? 
> 
> Or even unmirrored drives (er.. you mean, LV's)...?  Again, isn't that the 
> point?  Anything can be done one way or another offline, but having the 
> ability online is what LVM is all about.  Sure, the question is whether the 
> Linux implementation is really mature enough to do it without failure.

The LVM has been around since 2.3.30-something in the kernel. It was
around as a 3rd party patch from 2.1.something. I would put it as nearly
as mature as some of the HP-UX and AIX versions. The stability of any
LVM system is directly related to the proficiency of the admin :)

Now can it do it's magic without failure? As there are a flock of
potential gotchas, it requires some intense effort on the admin part to
carry it out glitch free. The main environment requirement is the
existence and use of a maintenance period where the system can be run in
a degraded mode to allow the resynching of a mirror. The extension of
the LV space currently requires the unmounting and remounting of the
filesystem being worked on. So databases must be stopped. HP-UX can,
with proper kernel patches and other stuff, extend a mounted partition
(slick!). At present, the Linux LVM can't. 
> 
> > Extending a logical volume is probably OK live.  Shrinking
> > is probably not. 
> 
> Shrinking, eh?  Even AIX doesn't do this.  Are they planning such support for 
> the Linux version?

It's not a highly useful feature, so probably not. It is easier to add
more space than move it around.
> 
> -E.
> 
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GPG ID: 829C6CA7 James P. Kinney III (M.S. Physics)
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