On Wed, 21 Jul 2004, Juhan Leemet wrote:

> Yes, that's true, I understand "fssnap" can be used to get a reliable and
> consistent backup for ufs filesystems, but...
>
> In this case, he has actually mirrored everything, right? He said
> "...configured DiskSuite to mirror root and the other disks."
>
> What about if he were to "metaoffline" his mirrors? One at a time, natch.
> Couldn't he then get a backup of a static "offline" mirror? Then when he
> puts the mirror back "metaonline" then it will sync up again. The man page
> for metaoffline even suggests this as a mechanism for doing online backups!

Yes, that would also work. Off the top of my head, I'm not sure
what all the pros and cons of fssnap vs metaoffline are, although
one obvioous benefit of the latter is that it'll work with any
file system, not just UFS (IIRC, only UFS supports fs snapshots
at present. I would be very surprised if DFS didn't, unless it
wasn't necesary by design...).

> I can't see any extra risk here, except perhaps on the "work in progress"
> while he has 1/2 mirror offline. If he loses one of the disks, he will
> either have the "static copy", i.e. like after restoring backup, or he
> will have the "real" dynamic copy, and he just syncs a new mirror.

True. And this risk can be mitigated by using 3-way mirrors.
That way, when you break off one of the sub-mirrors to back it
up, the "live" file system is still safe in a 2-way mirror.
It's one of those cost/benefits type of things.

--
Rich Teer, SCNA, SCSA

President,
Rite Online Inc.

Voice: +1 (250) 979-1638
URL: http://www.rite-online.net