zfs discuss - Oct 2009 - Mount ZFS on Dual Boot Machine (open)solaris

Hi,

Sorry if this is a dumb question but i can''t seem to find an anwser
anything close to what i am trying to figure out...

I have a dual boot machine with 3 disks -

2 x 1TB mirror OpenSolaris with ZFS root pool
1x 250GB Solaris 10 with ZFS root pool

This is a development\testing\home file server machine only.

My question is tho, since I can boot into either OpenSolaris or Solaris (but not
both at the same time obviousvly :) i''d like to be able to mount the
other disks into whatever host OS i boot into.

Is this possible & recommended? 

Is there any scope for inconsistency if say i upgrade OpenSolaris with new ZFS
versions but continue mounting a mirror in Solaris with old versions?

I guess i''m wondering if it''s possible if doing this could
corrupt one or the other?

Many thanks,
cam
-- 
This message posted from opensolaris.org

On 10/15/09 20:36, Cameron Jones wrote:
> My question is tho, since I can boot into either OpenSolaris or
> Solaris (but not both at the same time obviousvly :) i''d like to
be
> able to mount the other disks into whatever host OS i boot into.
> Is this possible&  recommended?
Definitely possible. Where do you keep your user data? It isn''t
clear that there is much utility in cross mounting rpools from
Solaris/sxce to Open Solaris; better to keep your user data in
one or more separate data pools and to just mount them. That
simplifies backups, too.
> Is there any scope for inconsistency if say i upgrade OpenSolaris
> with new ZFS versions but continue mounting a mirror in Solaris with
> old versions?
You have to watch out for the gratuitous update-archive problem
http://defect.opensolaris.org/bz/show_bug.cgi?id=11358 at
reboot. Otherwise AFAIK you just have to be careful. So far ZFS
seems to have kept backwards compatibility. Just don''t accidentally
do a zpool upgrade :-). Because of 11358, I would not recommend
cross mounting the rpools. But it isn''t clear that that is what you
really want to achieve...
> Many thanks,
> cam

thanks! 

by cross-mounting do you mean mounting the drives on 2 running OS''s?
that wasn''t really what i was looking for but nice to know the option
is there, even tho not recommended!

my only real aim was to have the 3 disks accessible when booting into either OS
so i could share archived data between them.

the solaris instance is only for testing so i haven''t got any real user
data in there, it''s just for messing around in and trying out things on
a real box before applying in production.

the opensolaris instance is what i am developing in and for archiving, backups
etc so would have this running most of the time.

it sounds like i shouldn''t have any problem cold-cross-mounting :)
although does bug 11358 only apply to opensolaris or would it also be possible
to apply to solaris 10 too?

also i thought i read in the doco that ZFS assigns an id to each drive which is
unique to the OS  - if i try to mount it into another OS would this id keep
changing each time i switch?
-- 
This message posted from opensolaris.org

On 10/15/09 23:31, Cameron Jones wrote:
>
> by cross-mounting do you mean mounting the drives on 2 running
OS''s?
> that wasn''t really what i was looking for but nice to know the
option
> is there, even tho not recommended!
No, since you really can''t run two OSs at the same time unless you use
zones. Maybe someone more expert than I could comment on the idea
of running OpenSolaris on a Solaris 10 or sxce host - e.g., in the case
of sxce, if they were both, say snv124?
  
> my only real aim was to have the 3 disks accessible when booting into
> either OS so i could share archived data between them.
That''s what you should do (and I do it all the time). Put your user
data a separate pool and import only that on both OS instances. So
in your case, install OpenSolaris in a 32GB or more slice 0 partition
of the mirror and /export on (say) slice 1. My data pool is called
"space"
and it has a number of file systems most of which are mounted on
/export (e.g., /export/home/userz for user "userz". You could do this
by zfs snap of the OpenSolaris rpool from Solaris, and then zfs recv
after running format (follow the guide for restoring a zfs rpool at
http://docs.sun.com/app/docs/doc/819-5461/ghzur?a=view).
> it sounds like i shouldn''t have any problem cold-cross-mounting :)
> although does bug 11358 only apply to opensolaris or would it also be
> possible to apply to solaris 10 too?
Not sure. sxce and Open Solaris both do the dreaded archive update,
so AFAIK Solaris 10 would do it too, possibly with bad consequences.
A workaround would be to make sure the other rpool is not mounted
when you reboot, but one whoops and you might be toast. Better to
keep data and OS  separate. Then you can do zfs snaps for rpool
backups and something different if you like for user data backups.
> also i thought i read in the doco that ZFS assigns an id to each
> drive which is unique to the OS  - if i try to mount it into another
> OS would this id keep changing each time i switch?
AFAIK it doesn''t. I have sxce and OpenSolaris running alternately
on one host and they mount the data pool with no problems at all. I
no longer even try to cross mount the rpools because my OpenSolaris
installs kept getting trashed by 11358, but at that time sxce was
on UFS. I believe the ids are assigned when the pool is created,
so if you zfs recv an rpool from another host with an otherwise
identical configuration, it will try (and correctly fail) to mount a
zombie data pool when you boot it. I assume the id is ignored
on the root pool at boot time or it wouldn''t be able to boot at all.
Undoubtedly a guru will chip in here if this is incorrect :-)

HTH -- Frank

On 10/16/09 09:29, I wrote:
>
> I assume the id is ignored on the root pool at boot time or it
> wouldn''t be able to boot at all. Undoubtedly a guru will chip in
here
> if this is incorrect :-)
Of course this was hogwash. You create  the pool before receiving
the snapshot, so the ID is local. One of the many nice things about
ZFS is that it is so logically consistent. I''d never want to go back!

Cheers -- Frank