Hello Holger,
I was actually missing your reply ;-)
> > What do you think?
>
> First of all, you keep saying "VM images", but you don't
> mention from which VM product. Nobody says VM images are
> simple file based images of what the virtual disk looks like.
[cut]
Yes, you are right and my customer has yet to give me some more specs
about *which product* is producing the VM images. But in the end, I bet
it won't matter too much because, as you said, those are "opaque
structures", not developed for rsyncability.
> Secondly, you say that the images are already somewhere, and
> your responsibility is simply to back them up. Hopefully,
> your client didn't have the smart idea to also encrypt the
> images and simply forget to tell you.
> Encryption would pretty much guarantee 0% rsync savings.
That's another point I have to clear with my customer.
> Thirdly, as long as things work as they are supposed to, you
> are probably fine. But what if something malfunctions and,
> say, your client mistakenly drops an empty (0 byte) file for
> an image one day (some partition may have been full and an
> automated script didn't notice)? The backup of the 0-byte
> file will be quite efficient, but I don't want to think about
> the next backup. That may only be a problem if the 0-byte
> file actually lands in a backup that is used as a reference
[cut]
Indeed, that would be a *big* problem!
And as you point at this kind of issue: it *did* happen to me, that a
customer moved a directory which contained about 20 GB of data!!!
> And within BackupPC may not be the best place to handle
> problems. For instance, if you first made a local copy of the
> images and then backed up that *copy*, you could script just
> about any checks you want to, use bandwidth limiting, abort
> transfers of single images that take too long, use a
> specialized tool that handles your VM images more efficiently
> than rsync, split your images after transferring ... it
> really depends on what guarantees you are making, what
> constraints you want (or need) to apply, how much effort you
> want to invest (and probably other things I've forgotten).
hehehe... I see what you're pointing at... I simply thought about using
BackupPC because I'm not doing anything else than configure an ssh
tunnel and rsync stuff trough it. But in this particular scenario, it is
not the best solution.
Thanks for your detailed thoughts, very helpful as usual! ;-)
Kind regards,
Flavio Boniforti
PIRAMIDE INFORMATICA SAGL
Via Ballerini 21
6600 Locarno
Switzerland
Phone: +41 91 751 68 81
Fax: +41 91 751 69 14
URL: http://www.piramide.ch
E-mail: flavio AT piramide DOT ch
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