[geeks] Cheap/reliable backup?

[microcode at zoho.com]

On Tue, Dec 03, 2013 at 05:00:06AM -0500, Mouse wrote:

> There's a page on English Wikipedia "Disk encryption theory" that talks
> about this stuff; that might be a decent place to start looking.  (And
> thank you very much for the compliment - though I fear you credit me
> with more expertise than I have; as a cryptographer I'm strictly a
> dilettante.)

I don't know what kind of a cryptographer you are, I just know you have a
much lower than average BS Quotient ;-) 

> 
> >> (At its simplest, consider a block cipher whose block size equals
> >> your disk sector size, used in ECB mode.  [...])
> > I understand that was just an example, but there aren't any known
> > block ciphers with a 512 bit block size AFAIK.
> 
> 4096 bit.  512 _byte_. 

Ok, but I'm still using old disks with 512 bit sectors.

> > We still can't do an incremental backup of a file, only of an entire
> > disk image or partition.
> 
> Well, if you're keeping disk-image backups, I would assume incremental
> backups would also be at the disk-image level.

Yes, but the discussion is meandering. I would be happy with archiving disk
images (I think). People mentioned incremental backups, which we already
use, etc. and which don't solve the question my particular problem is about
ie. if I want a disk image on optical storage I accept the limitation I'm
not going to be able to do incremental backups like that, at least not in
the sense of maximizing media utilization. 

> Actually, no.  My own backup paradigm is basically dd images, but the
> backup host neither knows nor case what filesystem (if any!) the client
> host has in the partition - it just stores the image as a big file in
> its own filesystem.  Incremental updates are sent as block contents,
> and a resync (eg, after a reboot) does not send the whole disk's
> contents over again.  (Currently it sends about 4% as much data as the
> disk holds; I have some ideas I need to implement to cut that down in
> common cases.)

Ok, but that is pretty unconventional and requires other pieces to get it
to work, and then (I don't have to tell you, I'm just thinking out loud) you
have to slap the blocks back in the right places in a disk (image) that *is*
a mirror of your source so you have to maintain meta-data and you are making
more work for yourself than if you let the filesystem do it.

> Of course, this is no immediate practical help to you unless that kind
> of incremental is suitable for your purposes, which it sounds as though
> it's not.

Too complicated for what I want, but if we think in the cloud direction that
people have been talking about I think it's kinda cool. I just want
something simple, like "this pile of BluRays is all I need." This table lamp
and this pile of BluRays, and that's ALL I need. 

--
        _                             _      
._ _ _ <_> ___  _ _  ___  ___  ___  _| | ___ 
| ' ' || |/ | '| '_>/ . \/ | '/ . \/ . |/ ._>
|_|_|_||_|\_|_.|_|  \___/\_|_.\___/\___|\___.