[Sunhelp] help disk mirroring

[Brian Scanlan]

On Fri, Jul 14, 2000 at 03:30:38PM -0500, Reagen Ward wrote:
> > Thanks to everyone who responded to my query. But i am confused. OS disk 
> > mirroring is good practice as i comprehend fron the replies. But what is the 
> > use when file system corruption on os disk is reflected on the mirrored disk 
> > as well.

The usefulness of disk mirroring is limited to not hoping your disk doesn't
fail, and a single head crash bringing your enterprise to a standstill, and a
small performance boost, as reads can be spread over two disks.

Solaris will, by default, panic on detecting file system corruption (correct
me if I'm wrong), though in Solaris 7 I see you can pass an option to mount so
as to not panic if corruption is detected - It'll simply unmount the
filesystem, and wait for it to be repaired by a fsck, which should fix the
corruption, unless caused by something awful like a broken disksuite setup
that's using the same disk partition in two seperate mirrors, or overlaping
partitions, wrongly setup through the format command.

> > May be i have failed in understanding. I would appreciate if 
> > someone can help me out on this.
> 
> Just keep a third disk out of the mirror, and either dd the filesystems to it,
> ufsdump them, or make it a part of a rotating mirror.

dd-ing a busy disk could result in a inconsistent state on the disk you've
made a copy to - ufsdump is better, you're best off putting the spare disk in
as a Disksuite mirror, syncing it, then pulling it out of the mirror.

I don't think filesystem corruption is very likely to happen using Sun's ufs
or VxFS, though, unless you regularly dd random stuff into your disks, and
insist on not panicing on detection of corruption, though I'm sure somebody's
got some horror story out there. ;)

Brian.
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