ZFS disk replacement questions

Mahlon E. Smith mahlon at martini.nu
Tue Nov 24 03:29:01 UTC 2009

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


Mahlon E. Smith  
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