raid of a concat in gvinum

Ulf Lilleengen lulf at
Tue Feb 5 06:36:27 PST 2008

On Tue, Feb 05, 2008 at 11:05:47AM +0100, Paolo Tealdi wrote:
> Dear all,
> I have a concat of three scsi disk ( 75GB + 75GB + 150GB) that works 
> without problems since 4 years using 6.2-RELEASE, i'll upgrade to 7.0 when 
> it will be released.
> I would like to change the configuration adding 2 more 300 GB disk and 
> creating a a big raid disk : (75+75+150) + 300 + 300 = 600 GB (a little 
> less).
> My questions are :
> Is this possible in gvinum ?
Adding disks to a volume is possible in a concatenated organization (jbod).
And your wish is also possible but not without copying data away and back.

> In other words, can i use for a raid a concatenated disk ?
I'm not entirely sure what you mean by this. By your calculation I assume you
want to do raid5 on the data. (Getting 300 + 300 + 300 where 1/3 is used for
parity allowing a total of 600GB disk space). You would have to your data in
order to do this (just take backup), but if you have that option, I would
perform the following operations:

1. Use the current concatenated volume you already have,
2. Create three new disks, one of them pointing to the volume and the two
other pointing to you new disks.
3. Create a raid5 plex and volume.

The additional configuration would be something like:

drive r1 device /dev/gvinum/<yourconcatvolume>
drive r2 device /dev/<newdisk1>
drive r3 device /dev/<newdisk2>

volume newdata
plex org raid5 493k     # This is the stripesize.
sd drive r1
sd drive r2
sd drive r3

I have not tried this myself, so I can't guarantee that it works.  I'd
appreciate if you send your current configuration so I can make sure my tips
here will be correct to your wishes.

> If yes, how ? Someone can point me to some examples or how-tos (googling i 
> didn't find anything to that specific configuration) ?
Documentation is a bit scarse, but the updated manpage I created during
Summer of Code contains some examples of gvinum use. Also see my example

> If i can do this (weird thing, i admit it :-) ) , must i destroy the 
> concatenated file system ? (my answer to this question is "yes, of course, 
> stupid", but ...)
Yes, and the reason for this is that the provider you already created, have
an active filsystem on it. Putting this provider in a raid-5 would require
parts of it be used for parity. If this was possible on the fly I wouldn't
recommend doing it without taking backup anyway.

As a last note, I recommend trying out my patches for gvinum in case you run
into any problems. It also contains the mentioned manpage-update. They can be
found here:
Currently I only have >= RELENG_7 patches though. I can generate
RELENG_6-patches if you really want :)

Ulf Lilleengen

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