On Thu, 31 Jul 2008 21:04:06 +0100, Orchid XP v8 wrote:

> Jim Henderson wrote:
> 
>> It sounds to me like they lack an understanding of "archival" vs.
>> "backup".
> 
> Precisely.
> 
> (There's also talk about how to "back up" our software so we don't lose
> it.)
> 
> Note also that there is a regulatory distinction between the two terms,
> and the government holds us to those regulations.

Then in your comments, you need to cite the regulations in particular, 
along with the "definitions" section (if it exists; most regulations do 
have some section somewhere that defines terms).

>> ISTR this is typically done this so you could do restores of individual
>> files; if you needed to restore the entire system, you'd have to pull
>> the last full backup from offsite storage.  It depends on the value of
>> the data if its lost.
> 
> Actually it seems to be so they don't have to bother actually attending
> to the machine except once a week. To my mind, leaving all the tapes
> right next to the server rather negates the entire purpose of daily
> backups. If we're going to play that game, why not just only back up
> once a week?

Well, actually, it doesn't negate the purpose of daily backups.  You're 
assuming (perhaps) that the backups are useful only in case something 
catastrophic happens to he building - like it burns to the ground (in 
which case, your argument is valid).  But "dumb user Joe Smith" deletes a 
file he needs or it gets corrupted - having the backup right there is the 
fastest path to recovery short of an undelete utility (which can have 
their own problems).

> [Yeah, I realise it's not *quite* the same, but you see what I'm
> saying.]

Yeah, but that scenario is a single use case out of a few.  When 
structuring your arguments, you don't want to pick a specialized low-risk/
high-cost scenario and use that as the basis for your argument.

>> Agreed.  That said, doing a restore is much better than depending on
>> the tape drive's report during the backup of problems.  I've been
>> burned by that - it said data was being written, but it was unreadable
>> due to tape errors.
> 
> Standard procedure is to record the data, rewind the tape, read back all
> the data and check it actually matches what's on disk, not just that the
> checksums on the tape are OK. Still, it seems reasonable to go a step
> further and actually test the thing "for real" by actually performing a
> backup. I'm not sure it needs to happen every 3 months though...

That is a reasonable procedure IME.  A full restore on a regular basis 
isn't a bad idea, just to rule out the tape drive lying on its read 
test.  Incidentally, that's what I believe happened to me just before a 
catastrophic disk failure on a finance server that was followed by the 
realisation that we could not restore ANY of the data from the tapes 
because the tapes were part of a bad batch - and the software we used was 
too stupid to skip over read errors on a restore, but instead would abort 
the restore completely.

Even still, we did manage to recover 3/4 of the data with some help from 
the software vendor.

>> Just Invis' description sounds like GFS style backups.  It's a style
>> that some people find difficult to describe.
> 
> Yeah, it's GFS. However, the chart they supplied seems to indicate that
> there is only one grandfather tape, only one father tape, and only one
> son tape. In other words, if you want to restore from 2 days ago, the
> tape has already been overwritten. Like, WTF? So clearly that can't be
> what they mean. Hey, it's not like anything is *labelled* or anything
> like that...

Well, it depends partly whether incrementals are used for the F & S or 
differentials are used.  If a differential tape is done (ie, since the 
last F or G, depending on whether we're talking about the S or F tape), 
then it picks up all changes since the last "full" backup (ie, G or F 
tape).  I would probably prefer to use at least 2 tapes in the rotation, 
though when using differentials - if the write to the tape bombs the 
second time around, then you've also overwritten your earlier 
differential and you lose that much more data.  With two, you at least 
can go back to the previous day.

> As I asserted, it probably made perfect sense to the guy who scribbled
> it down.

Very likely.  One thing I do in situations like that is try to restate 
what has been stated and ask if my understanding is correct.  That 
usually helps the writer - especially if what you repeat back isn't what 
was meant.

Jim

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