Just to be clear: Any LTO generation will read and write one generation
back and will read two generations back. So an LTO-4 drive will read and
write LTO-3 tapes and read LTO-2 tapes.

There is no forward compatibility. An LTO-4 tape inserted into an LTO-3
drive -- whether manually or by a jukebox -- will not load; it will
simply eject. It's essentially the same as inserting a cleaning tape but
much faster. There is no chance of an LTO-3 drive writing anything to an
LTO-4 tape.

So all the advice you've received here is good. As Frank said, you have
to create separate pools for your LTO-4 drives and tapes and your LTO-3
drives and tapes. And as Bingo pointed out, mixed media is not supported
and you have to control the loads for operations like labeling and
restores. Left to its own devices (pun intended), NetWorker may well try
to insert an LTO-4 tape into an LTO-3 drive. That wouldn't be
catastrophic. No data would be overwritten, but the drive may end up in
Service Mode.

Good luck!

Conrad Macina
Pfizer, Inc.


-----Original Message-----
From: Eugene Vilensky [mailto:evilensky AT GMAIL DOT COM] 
Sent: Tuesday, August 16, 2011 5:19 PM
Subject: Re: Current state of mixed media in library?

On Tue, Aug 16, 2011 at 3:49 PM, bingo
<networker-forum AT backupcentral DOT com> wrote:
> In fact i don't even know whether an LTO4 tape can be written by a
LTO3 drive at all. But assuming that it is possible, you might then run
into another problem if you insert it back into a LTO4 drive. This will
now verify a tape written with lower density and due to firmware, it
will use the density found which means that you will never again be able
to change to the max (LTO4) density unless you erase the label with an
unconditional overwrite like tapeexercise.


Surely there are firmware restrictions on what a drive will/will not
attempt to do newer generation media that it does not support?  Isn't
that partly what that little 16K chip inside the cartridge for?

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