ZFS disk replacement questions

[Mahlon E. Smith]

On Tue, Nov 03, 2009, Derrick Ryalls wrote:
> On Tue, Nov 3, 2009 at 10:21 AM, Steve Polyack <korvus at comcast.net> wrote:
> > Derrick Ryalls wrote:
> >>
> >> 1) In the event of a disk failure, how do I trace back the name such
> >> as adX to a physical drive in the enclosure?  Is there a way to take
> >> the drive offline then use atacontrol to spin it down or something so
> >> it is easy to identify?
> >>
> >
> > In my opinion you are best off using glabel(8) to give names to the disks.
> >  This way you can name them in a way that makes sense to you.  Additionally,
> > when you create the ZFS pool you will use the glabel'd names.  This means
> > that the pool will still come up properly if something causes your devices
> > to be numbered differently (i.e. a drive dies and you happen to reboot the
> > system).
> 
> I believe ZFS does this automatically.  Supposedly, if you take a
> working set of RAIDZ drives from one machine and put it in another,
> ZFS will figure out the drives since they get labelled by ZFS
> internally.  My question concerns how to identify the physical disk in
> question based on the adX or glabel name?  Different name in software
> is fine, but if the drive fails I want to make sure I pull the correct
> drive.



This is only true if the metadata on the drives is re-read -- if your
pool loses a drive and the device numbers shuffle, your pool will be
FAILED on the next boot.

You can, however, force the metadata to be re-read via a 'zfs export
POOL', and a subsequent 'zfs import POOL'. 

However, using glabel avoid that step entirely, as ZFS will always see
the 'right' devices in the right places, regardless of where they are
physically.

-Mahlon

--
Mahlon E. Smith  
http://www.martini.nu/contact.html
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