Error correction with aes-looback / cryptoloop?

[Anthony de Boer]

Mike Oliver wrote:
> Quoting Anthony de Boer <adb-tlug-AbAJl/g/NLXk1uMJSBkQmQ at public.gmane.org>:
>> There are critical bits like the superblock and the directory at the root
>> of the partition, but alternate superblocks and fsck can affect at least
>> partial recovery from many errors.
>
> Yeah, that's a point.  How much space do those occupy?  And do they change
> as I add/remove files?  It would be nice to be able to back up a small 
> piece
> to protect against errors there.

Two principles that have served me well in a lot of years with Unix/Linux:

I Can Look That Up - manpages, or look in the Documentation or fs/ext*
directories in the kernel sources, or the e2fsprogs sources.  Knowing
what's where and having a good grasp of the bits you need to frob in
normal use beats rote memorization of all the trivia you can find.

I've Never Needed To Look That Up - there are a *lot* of things you never
look inside until they've either broken or demonstrated the need of some
vital additional feature.  Stuff that's never come to my attention in
that way indicates the authors (Remy Card, Ted Ts'o, Stephen Tweedie, and
a cast of many, in this case) have done a fine job.

Ext2 and its heirs keep duplicate superblocks at intervals, and there is
a mount option to use a different one if the default one at the start of
the device gets broken.  Probably no need to specifically back that up,
then.

>> And you *ARE* going to keep backups, right?
>
> Well, sure, from time to time.  But I don't back up every day or anything;
> too much of a PITA.

Using something like rsync to copy from a laptop to your server or
desktop periodically, especially with the commandline captured in a
shellscript to make it easy to fire off, can make it easy to back things
up when you're connected and have a spare moment.  There's also a tool
available called unison that can be used to bidirectionally sync
important files between eg. a laptop and desktop so that you can work on
them in either place, and thereby also survive the death of either copy.

A lot depends on what sort of work you do; if you're a digital camera
buff then you may want to back up specifically after downloading new
pictures from your camera, if you're a programmer then a backup upon
completion of a program milestone (or just keep a git/cvs/svn/whatever
repository on a different box), that sort of thing.

-- 
Anthony de Boer
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