zfs on gmirror slice

[Thomas Backman]

On Sep 2, 2009, at 10:27 AM, Mark Stapper wrote:

> Emil Mikulic wrote:
>> On Wed, Sep 02, 2009 at 09:20:21AM +0200, Mark Stapper wrote:
>>
>>> updating a zfs filesystem which you are running from is next to
>>> impossible.
>>>
>>
>> [citation needed]  :)
>>
> Well, to update your zfs filesystem version, the filesystem is first
> unmounted, then updated, and then mounted again.
> citation coming up!
> # umount /
> umount: unmount of / failed: Invalid argument
Nothing a LiveCD or something to that regard can't handle. Obviously  
this doesn't work for everyone, but it should for many.

>>
>>> So, i would recommend setting up gmirror to mirror your whole disks,
>>> install the base system(boot and "world") on a small UFS slice,  
>>> and use
>>> the rest of the disc as zfs slice.
>>>
>>
>> As Thomas Backman pointed out, this means you won't get self-healing.
>>
> self-healing sounds very nice, but with mirrorring you have data on  
> two
> discs, so in that case there no "healing" involved, it's just
> checksumming and reading the non-corrupted copy.
> From the gmirror manpage: "All operations like failure detection,  
> stale
> component detection, rebuild of stale components, etc. are also done
> automatically."
> This would indicate the same functionality, with a much less fancy  
> name.
> However, i have not tested it the way they demonstrate zfs's
> "self-healing" property.
> I might, if I get the time to run it in a virtual machine one of these
> days..
If ZFS finds a corrupted copy and a non-corrupted one in a mirrored  
ZFS pool, it will repair the damage so that both copies are valid, so  
yes, self-healing will indeed occur. :)

Regards,
Thomas