[H-GEN] Tape Drives

Jason Henry Parker jasonp at uq.net.au
Sat Jan 5 21:27:08 EST 2002


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"Frank Brand" <fbrand at uq.net.au> writes:

> Ever since hard drives have become reasonable in price it has been
> my belief that removable hard drives are better value than tape
> decks.

Well, considering that the main point of backing anything up is to not
have any data loss when, say, a disk's head decides to meet the disk
surface, or a bearing decides to seize up, I really do not see the
point of using another drive, especially a removable which is going to
be subject to stresses as it is removed, inserted and transported.

That said, one thing I've done is to set up another machine---it
doesn't need to do anything but this---and run rsyncs from the
backed-up host to it every few hours.  It buys another copy of your
files, and smart users can even be taught to do their own restores.
The downside is the cost in CPU and maintenance, not to mention the
amount of time needed to make *sure* it's working correctly.

Rsync's a nice tool, but don't overdo it.

> Here is one possibility based on a two week cycle but maybe if you are doing
> accounting stuff you might need to keep for a full month or a financial
> period of some sort.

I suppose this is why people like Grandfather-Father-Son so much:
it's pretty simple to remember, and thus easy for a single operator to
manage by hand.

Personally, I prefer to use AMANDA and let the computer work out when
to back up what (of course, this isn't exactly trivial either, there
being plenty of options, and AMANDA can use an annoying number of
tapes at times, but John R Jackson is hard to argue with!).

I cannot stress enough how important it is to think---hard---about
your backup scheme.  Trace through it for a month, asking at each step
`Okay, what if this tape/disk/tape drive/whatever is corrupted, or
lost?'.  You'll be terrified to think of just how much pain you have
to go through to have backups that can truly be depended on.

One thing I mentioned to Pat last night that bears repeating here is
that *in theory* it's a good idea to have two tape units.  If the unit
used to write your backups has a head misalignment, and the unit dies,
then unless you can find another unit that has the same head
misalignment you are essentially up the proverbial creek.

You'll need to run regular backup tests (you'd need to do this with
removable disks, too):  verify your backups by:

 * ensuring they can be read from the media
 * checking they have a copy of every file on the disk
 * checking every file on the media has a corresponding file on disk
 * checking every file's copy is the same as the one on disk
 * checking you do, in fact, know how to restore
   + a single file
   + a whole directory tree
   + your root filesystem (ie where your backup records are kept,
     probably)
   + the rest of your filesystems from that point.

You don't want to have to work any of that out when the company is
hemorrhaging money because the file server is down and no-one can do
their work.

> Maybe other people have different ideas.

About backups?  You bet.  The whole topic is only slightly less
contentious than `which editor should I use?'.

As a parting note, I'd like to point out that even though I may sound
like an expert who has all this worked out and running perfectly, I'm
not.  I've spent the better part of 2001 watching and learning about
backups, and a good fraction of the holiday break learning *just how
good* (or bad) my ideas about backing up data have been.

jason
-- 
||----|---|------------|--|-------|------|-----------|-#---|-|--|------||
| Men are Figs!                               http://linux.org.au/conf/ |
|                   --Ann Burlingham                   jasonp at uq.net.au |
||--|--------|--------------|----|-------------|------|---------|-----|-|

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