You mentioned one issue; the 220s can't read tapes written in 320s.

Another serious issue is that the 220s can't append to a tape in 320 format.
If a media server has access to both drive types, but they're the same
density in netbackup, you can't guarantee that when it grabs the tape half
filled from the night before on a 320 drive, that it won't put it in a 220
drive and try to finish writing to it... if it does, it's not going to like
it.

A less serious issue is that when a 320 appends to a tape in 220 format, it
does so at 220 speeds, so you lose out on the faster capabilities of the 320
drive.  I believe the format of the tape is put back as 320 when netbackup
relabels it when the tape is unassigned and re-assigned and starts from the
beginning again.  There is a light on the front of the 320 drives that will
tell you if it's running in 220 mode.

Since there is no way to manually set the 320 drive in 220 mode and have it
stay that way across tape mounts/unmounts and STK won't sell new 220 drives,
it's an issue.

You have to...
1.) look at refurbished drives
2.) keep the 220s and 320s in separate robots with separate sets of tapes
3.) specify a different density for the 320s and deal with managing two
different densities of tapes within netbackup, even though they're the same
physical tape.

BTW: We tried using a 320 drive to restore a tape in 220 format during a DR
test and the performance was absolutely horrible (as in so bad it was
unacceptable). We had them switch out the 320 drive for a 220 drive and
everything ran perfect after that.  Didn't get a chance to test it once we
got back from the trip though... don't know if it was a bad drive (but if I
remember right, we tried two different 320 drives first) or if there is a
huge performance hit when doing the backward compatible reads.


- Scott

-----Original Message-----
From: Thomas Tschida [mailto:Thomas.Tschida AT udlp DOT com] 
Sent: Thursday, June 24, 2004 2:40 PM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: [Veritas-bu] SDLT compatibility

Hello All,

We are in the process of adding drives to our StorageTek L700.  We currently
have 12 SDLT 220s, and we are adding 6 SDLT 320s.

We have SSO licenses for all 18 drives.  The issue is that the 220s can't
read tapes written with the 320 drives.  From what I can predict, this would
only be an issue for restores.  If that's true, is there a way to force Net
Backup to use specific drives for restores?

Any info is appreciated.

Tom Tschida
United Defense


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