On Tue, Nov 13, 2012 at 6:16 PM, Karl Wagner <k...@mouse-hole.com> wrote:
> On 2012-11-13 17:42, Peter Tribble wrote:
> > Given storage provisioned off a SAN (I know, but sometimes that's
> >  what you have to work with), what's the best way to expand a pool?
> >
> > Specifically, I can either grow existing LUNs, a]or add new LUNs.
> >
> > As an example, If I have 24x 2TB LUNs, and wish to double the
> > size of the pool, is it better to add 24 additional 2TB LUNs, or
> > get each of the existing LUNs expanded to 4TB each?
> This is only my opinion, but I would say you'd be better off expanding your
> current LUNs.
> The reason for this is balance. Currently, your data should be spread fairly
> evenly over the LUNs. If you add more, those will be empty, which will
> affect how data is written (data will try to go to those first).
> If you just expand your current LUNs, the data will remain balanced, and ZFS
> will just use the additional space.

Maybe, or maybe not. If you think in terms of metaslabs, then there
isn't any difference between creating extra metaslabs by growing an
existing LUN and creating new LUNs. With pooled storage on the
SAN back-end, there's no difference in I/O placement either.

Peripherally, this note by Adam Leventhal may be of interest


-Peter Tribble
http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/
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