Using GTP and glabel for ZFS arrays

[Dan Langille]

On 7/23/2010 10:25 PM, Freddie Cash wrote:
> On Fri, Jul 23, 2010 at 6:33 PM, Dan Langille<dan at langille.org>  wrote:
>> Pawell and I had an online chat about part of my strategy.  To be clear:
>>
>> I have a 5x2TB raidz1 array.
>>
>> I have 2x2TB empty HDD
>>
>> My goal was to go to raidz2 by:
>> - copy data to empty HDD
>> - redo the zpool to be raidz2
>> - copy back the data
>> - add in the two previously empty HDD to the zpol
>>
>> I now understand that after a raidz array has been created, you can't add a
>> new HDD to it.  I'd like to, but it sounds like you cannot.
>>
>> "It is not possible to add a disk as a column to a RAID-Z, RAID-Z2, or
>> RAID-Z3 vdev." http://en.wikipedia.org/wiki/ZFS#Limitations
>>
>> So, it seems I have a 5-HDD zpool and it's going to stay that way.
>
> You can fake it out by using sparse files for members of the new
> raidz2 vdev (when creating the vdev), then offline the file-based
> members so that you are running a degraded pool, copy the data to the
> pool, then replace the file-based members with physical harddrives.

So I'm creating a 7 drive pool, with 5 real drives members and two 
file-based members.

> I've posted a theoretical method for doing so here:
> http://forums.freebsd.org/showpost.php?p=93889&postcount=7
>
> It's theoretical as I have not investigated how to create sparse files
> on FreeBSD, nor have I done this.  It's based on several posts to the
> zfs-discuss mailing list where several people have done this on
> OpenSolaris.

I see no downside.  There is no risk that "it won't work and I'll lose 
all the data".

-- 
Dan Langille - http://langille.org/