Mirror of Raidz for data reliability

[Marcelo Araujo]

2012/5/15 Paul Schenkeveld <freebsd at psconsult.nl>

> On Mon, May 14, 2012 at 01:35:51AM +0800, Marcelo Araujo wrote:
> > Hi All,
> >
> > Me and a co-work are working in a new feature for ZFS, we have 2 Machines
> > and 2 JBOD, every Machine are connected on those JBOD via SAS and we are
> > trying to make a fail-over server. Currently every each Machine has two
> SAS
> > cables, each one connected in both JBOD.
> >
> > We have worked last week to figure out, how we could make the data be
> > always alive in case one JBOD dies, and let me show you my console output
> > ;):
> >
> > controllerA# zpool status -v araujo
> >   pool: araujo
> >  state: ONLINE
> >  scan: resilvered 57K in 0h0m with 0 errors on Sat May 12 14:32:29 2012
> > config:
> >
> >         NAME          STATE     READ WRITE CKSUM
> >         araujo        ONLINE       0     0     0
> >           raidz1-0    ONLINE       0     0     0
> >             mirror-0  ONLINE       0     0     0
> >               da0     ONLINE       0     0     0
> >               da3     ONLINE       0     0     0
> >             mirror-1  ONLINE       0     0     0
> >               da1     ONLINE       0     0     0
> >               da4     ONLINE       0     0     0
> >             mirror-2  ONLINE       0     0     0
> >               da2     ONLINE       0     0     0
> >               da5     ONLINE       0     0     0
> >
>
> Maybe a dumb question, how you you create the above setup?  I seem unable
> to create a raidz consisting of mirrors neither can I attach a second
> physical drive to an existing one in a raidz of three single drives:
>
>  # zpool create tank raidz1 mirror /dev/da0 /dev/da3 mirror /dev/da1
> /dev/da4 mirror /dev/da2 /dev/da5
>  invalid vdev specification: raidz1 requires at least 2 devices
>
>  # zpool create tank raidz1 /dev/da0 /dev/da1 /dev/da2
>  # zpool attach tank /dev/da0 /dev/da3
>  cannot attach /dev/da3 to /dev/da0: can only attach to mirrors and
> top-level disks
>
>  # zpool upgrade
>  This system is currently running ZFS pool version 28.
>
>  All pools are formatted using this version.
>
> Kind regards,
>
> Paul Schenkeveld
>

Hey Paul,

Yes, I'm using the latest version with code modification, it might be a new
feature.
The currently ZFS doesn't support this kind of set, that was I ask, if
there is another way that I supposed to don't know and could do the same
thing.

If it make sense, maybe, I'll put more effort to bring this kind of stuff
as a new feature. However, it is not so simple that I could made in few
days as well as have this feature only on FreeBSD, it will make the code
inconsistent between our ZFS port and Illumos-gate.

But is interesting.

Best Regards,
-- 
Marcelo Araujo
araujo at FreeBSD.org