Veritas-bu

[Veritas-bu] last image expiration date on a tape

2005-06-20 16:47:28
Subject: [Veritas-bu] last image expiration date on a tape
From: Mark.Donaldson AT cexp DOT com (Mark.Donaldson AT cexp DOT com)
Date: Mon, 20 Jun 2005 14:47:28 -0600
You need to use more tapes, in my opinion.  The tape is not marked as empty
and available until the last image on that tape expires.  By "last", I mean
the one with the longest retention time, not the one at the end of the tape.
If they're all the same retention period, then, of course, that's the last
on the tape, too.

You can't overwrite expired images at the beginning of the tape while
waiting for the images at the end of the tape to expire.  If you manually
expire the images at the end of the tape early, then you're not really
keeping X days of retained images, right?  If Joe Blow comes to you tomorrow
& asks for a 3-day old file, and you expired it to make a tape empty, you
may be danger of a CLM (a Career Limiting Move).

If you're switching tapes every day, which is a good policy in my opinion to
prevent many days of loss in the event of media failure, then tape A,
written yesterday won't expire for 6-days (assuming a 7-day retention).
Tape B, written today, won't expire for 7 days.  When tape A is full, then
you're kind of stuck for 6 more days waiting for remaining image on it to
expire.  

You have limited choices in this case: Expire the remaining images on A to
free up the tape and make it writable.  This, IMO, is bad because you've
violated your retention policy.

What you need is a Tape C, to replace Tape A while it's aging.  The trouble
for your onsite guy is knowing when to use Tape C and shelve tape A.  For
this you need a report that is mailed to him that say, OK - shelve A & use C
until further notice.  Of course, if A is full and your backups are of
near-consistent size, then B is about to become full for the same reason and
you're going to need tape D real soon, too.

OK, so here's how I'd do this.  I'd get 10 tapes, assuming a one-week
retention, and label them 1 to 10.  Every day the onsite guy replaces tape X
with tape X+1 (rolling around, of course from 10 to to one,  mathematical
modulus & all that happy stuff).  You've got built in aging and an easy
method of tape tracking.  When tape 1 fills, it'll 10 days before it's used
again and it'll be fully expired.

The main idea is that if you're going to do a salt-and-pepper method of tape
handling, as I said, a good idea, then you're going to need more than two
tapes.  What you really need is (retention-period + 1 day) tapes but 10 is a
nice round number.  Don't be stingy on tapes if you can help it.

HTH - M

-----Original Message-----
From: veritas-bu-admin AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]On Behalf Of Iain Miller
Sent: Sunday, June 19, 2005 3:18 AM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] last image expiration date on a tape


Guys,

I have inherited a netbackup server (4.5) running on Solaris 8.  There
is no library attached only a single tape drive - we use an on site
person to switch tapes every day.

My main question is - How do I get images that have expired on the
media overwritable??

I have replaced all the tapes in the cycle and I have now filled my
first piece of media - even though the images have expired, they are
still on the tape and I can't overwrite them.  We use the same tapes
on a weekly basis, so there are newer images on the tape that haven't
expired yet.  I guess that they could be manually expired, but is
there a neater way to do this??

I had thought about reducing the retention period down to 6 days (so
that when  the tape is inserted after a week, the images will expire
and I should be able to overwrite them).  Anybody have any thoughts /
feelings about how best to achieve what I am looking for.

As usual, thanks in advance for any suggestions.

Regards,

Iain.

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