On Tue, Sep 16, 2008 at 04:41:04PM +0800, John Morris wrote:
> Dustin J. Mitchell wrote:
> >On Mon, Sep 15, 2008 at 11:36 PM, John Morris <jman AT ablesky DOT com>
> >wrote:
> >
> >>My question is, is this actually a good idea? Will there be any problems
> >>I
> >>haven't anticipated, such as the two configs conflicting? For example, I
> >>notice that there is only one /etc/amandates file that is presumably
> >>shared
> >>by both configurations. I don't know whether the date to begin
> >>incrementals
> >>from is from this file or from /var/lib/amanda/gnutar-lists.
> >>
> >
> >No, it isn't a good idea, because there's a better solution that
> >doesn't involve this sort of gymnastics: RAIT. You can set up a RAIT
> >between the two tape devices, and then even if a drive is down, your
> >recoveries will work fine.
> >
> >Dustin
> >
>
> The configuration I describe solves some problems that RAIT won't. See
> if there's any error in my reasoning here.
>
I'll add another yes to Dustin's and Chris' suggestion of RAIT.
> The two configurations run on alternating days. One configuration runs
> more often (3 days/week) on a smaller disk, so these backups only go
> back a month. The other configuration runs less often (2 days/week) on
> a larger disk, so these backups go back two months. With RAIT, you get
> one configuration that stores identically replicated data, so there's no
> opportunity to tweak one copy to go back further in time (is this true?).
This is not the same thing but may have some benefits. If your average
daily backup size is smaller, you would be able to retain more daily
backups in the same disk space. Typically that would be done by
lengthening the dumpcycle. Maybe that is not appropriate for all DLE's
you define, but keep in mind that dumpcycle can now be defined for
individual dumptypes. So if you can lengthen the dumpcycle for some
basically static DLEs, maybe you can increase the total number of dumps
being retained.
Two examples of where I've used this technique are a file system I
used to contain CD and DVD .iso files and another containing only
copies of equipment user guides and other reference material. Neither
ever changes unless I added something. So month long dumpcycles were
not a problem. Sometimes when I've added a cd/dvd image and it kept
getting backed up by the incrementals, I forced an early level 0 on
that DLE. I mean how many backup copies of fedora.iso do I need? ;)
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
12027 Creekbend Drive (703) 787-0884
Reston, VA 20194 (703) 787-0922 (fax)
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