Half a Mirror Backup

Julian H. Stacey jhs at berklix.com
Sun Jan 2 21:28:13 UTC 2011

David Brodbeck wrote:
> On Sun, Jan 2, 2011 at 11:56 AM, Jason C. Wells <jcw at speakeasy.net> wrote:
> > Is using one half of a mirror as a backup a good/bad idea?
> >
> > I was thinking of rotating drives on a periodic basis as a back up method.
> >  You'd get the backup instantly, but rebuilding the mirror with the incoming
> > drive would take a little time and leave you vulnerable to a small loss of
> > data if a disk failed while the mirror was rebuilding.
> Besides the problem you mention, you'll have a pretty sizable
> performance hit while the mirror is being rebuilt.  Also, keep in mind
> that the most likely time for a second drive to fail is during a
> rebuild, since the rebuild forces a read from every sector.  I think I
> would use rsync or dump instead, although I have to admit the rotating
> mirror idea is clever.

Ref rsync:
Personally I use rdist6, (from familiarity=habit rather than conscious
choice, (it's more limited predecessor rdist, has been in BSD a Long time))

But beware: rdist6 fails on files bigger than 2G on i686 but (not
on amd64, on amd64 no problem), I wouldnt know if rsync might have
a similar 2G restriction.

Julian Stacey, BSD Unix Linux C Sys Eng Consultants Munich http://berklix.com
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