whats best pracfive for ZFS on a whole disc these days ?

[Stefan Bethke]

Am 15.11.2009 um 00:58 schrieb Larry Rosenman:

>>> On Wed Jul 15 at 16:22, Freddie Cash <fjwcash at gmail.com> wrote:
>>> Yep.  It's as simple as:
>>> 
>>>  * label all the drives using glabel, while they're still attached to
>>> the pool
>>>  * use "zpool replace pool ad4 label/disk01" to replace 1 drive
>>>  * wait for it to resilver
>>>  * use "zpool replace pool ad6 label/disk02" to replace the next
>>> drive
>>>  * repeat the resilver and replace until all the devices are replaced
>>> 
>>> This is what I did to one of our servers.  Works quite nicely.
>>> 
>>> There's no need to detach anything.
>> 
>> I'll try it when I get home and see how it goes.
> 
> When I try that, I get:

> # glabel label disk01 /dev/ada1
> glabel: Can't store metadata on /dev/ada1: Operation not permitted.

There's some caveats that you need to consider before attempting this: most importantly, glabel will re-use the last block of the disk/partition to store the label.  Apparently, in many cases, the filesystem (UFS, ZFS) allocates blocks in larger chunks (8K or larger), and the last few blocks are unused and can be repurposed.  But there's no guarantee, so you might damage the filesystem by labeling the device.  I don't understand enough to definitivly say how to deterime whether the last block is available or not, so make sure you have a backup before trying.

Secondly, my limited experience shows that both GEOM and ZFS can get confused about devices/partitions/geoms that start on the same block as others.  How these are picked up by GEOM and/or ZFS in their probing depends on the order, and it wasn't always obvious to me how that worked.  In one case, I couldn't get GEOM to pick up the /dev/label entry, since it removed the label entry as soon as the physical device node was probed.  I've since come to the conclusion that labelled GPT partitions are the way forward, and now that booting off ZRAID pools on GPT partitions works, there's little speaking against it, IMO.

Finally, if you want to label the existing disks, you probably need to take the pool offline for the labelling step, using zpool export, so the devices are not mounted anymore.


Stefan

-- 
Stefan Bethke <stb at lassitu.de>   Fon +49 151 14070811