Tao Of Backup Wailing Wall Story
Even if you have a perfectly good backup, you may *not* be able to restore it.
OK, so it was my own fault. I fiddled around with my PGP keys and
lost the private part of one main key (thought I had made a backup
of the key, but only saved the public part). Only found out about
it when I tried to uncrypt a file containing some personal e-mails
No problem, I thought, my company does a backup of everything on a
daily basis, and they keep montly snapshots for over a year,
so let's just restore the keys from a backup before the erasure.
Problem was, the Computer Department only kept the *index* files
for their backups for the past few weeks, so they were unable
to exactly locate on which tape the file could be found. No
problem either (or so I thought), they just needed to scan the
relevant tapes (3 tapes, 40G each) for the file.
Well, I finally got a call that they were unable to find that
particular file without investing further manpower, which would
have to be paid by our department.
Turned out that there was only one tape drive available for both
reading and writing the backups, and due to the long scanning
time the sysop would have to come in rather early just to insert
the tape so the scan would be finished by evening, when the daily
backup was scheduled.
Needless to say, due to the "inofficial" status of my usage of PGP,
no funding was available, so the key file is still not restored.
I thus have lost some information that is not of interest for my
company but still invaluable for me.
* _You_ are responsible for your personal data, don't assume that
normal company procedures will guarantee the safety of your
personal files. Do backups of critical data by copying files
to a different file system.
* Have redundant backup hardware available, so backup and restore
can be done independently, without one blocking the other
(but also see next point).
* Check your backup *hardware* regularily (I'm missing this point
in the Seven Heads of Backup Tao). Write backups with one
tape drive and verify them on the other drive, so no hardware kink
(like a misadjusted head) can render your backups unreadable
(at a later time, after the drive got repaired).
[We had that case with a CD writer: backups (or rather snapshots)
of software release versions written with that writer were
unreadable on a standard CD drive. We found out half a year later.
Luckily, no damage was done.]
* And last but not least: keep old backups in a useful state. Save
those indices on a different medium (e.g. CD Rom) with (semi-)direct
access. Most "desasters" are localized, so it certainly is more
economical to be able to do a partial restore rather quickly than
to have to rescan all those gigabytes.
Sat 26-Sep-1998 8:57am