Not sure if this will make it to the list, but I'll try...

On 11/13/12, Peter Tribble 
> 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?

The thing I've found about growing the LUN is to evaluate if it saves you time 
and effort in your setup to make it work. So, first I figure out if it's 
possible. Then I figure out how big a PITA it is compared to the PITA of 
allocating new LUNs. For example I've got one SAN backend here where it's easy 
as pie (lun resize blah and then OS steps) and another backend where it 
requires a major undertaking (create temporary horcm files, destroy mirrors, 
run special command to resize mirror, wait, run special command to resize 
source, wait, recreate mirrors, delete temporary horcms, etc etc and *then* the 
OS steps).

What I love about ZFS is that it can handle either approach.

So it depends on your setup. In your case if it's at all painful to grow the 
LUNs, what I'd probably do is allocate new 4TB LUNs - and replace your 2TB LUNs 
with them one at a time with zpool replace, and wait for the resliver to finish 
each time. With autoexpansion on, you should get the additional capacity as 
soon as the resliver for each one is done, and the old 2TB LUNs should be 
reclaimable as soon as it's reslivered out.

That being said, I'm not aware of what any deeper implications of doing that 
are - from what Karl said about balancing the data out as one example.



> -- 
> -Peter Tribble
> -
> _______________________________________________
> zfs-discuss mailing list



Brian Wilson, Solaris SE, UW-Madison DoIT

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