Ditto.

The LTO spec is backwards compatible. LTO4 doesn't remove capabilities
it adds them which is the reason you can read/write to a LTO3 tape and
read LTO2/3. The minimum stream rate is the same as LTO3. 

Remember LTO is an Open Standard. Even though each vendor may tweak
their drives they all must meet the same specification adopted for LTO.

.

Thanks,

Dana


-----Original Message-----
From: EMC NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU] On
Behalf Of Curtis Preston
Sent: Thursday, January 17, 2008 2:44 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: Recommendations for new tape library?

A> My vendor got me a list of the supported streaming modes for LTO3
A> and LTO4, and the lowest mode on 4 was actually less than the
A> lowest on 3 (somewhere around 15MB/s or so from memory).

Lies.  LTO-4's minimum speed is the same as LTO-3's, just under 30 MB/s.
And, remember, this isn't an infinitely variable speed.  It's 30, then
50, then 100, or something like that.  If you're going faster than 30,
it's going to go 50, etc.  This means you'll rarely truly match the
speed of your drive.

>I've been told that the HP LTO-4 drives can ratchet back their
>streaming speed in a linear manner from max down to 0, but I'm not
>sure I believe it.

Don't believe it.  Whoever said that is out right lying.  If that were
the case, they would be shouting this from the roof tops.

I will say it again, this time in caps.

IF YOU ARE BACKING UP TO A TAPE DRIVE AND NOT USING IT TO ITS FULLEST
RATED SPEED, YOU ARE WASTING YOUR MONEY.  I have people that are using
tape to its fullest, but at speeds over 100 MB/s, it's really hard to do
so directly, and EXTREMELY hard to do so when backing up across the
network -- and you'll be using insane multiplexing settings to do it.

If you want your primary repository of backups to be tape, at least buy
a properly designed disk staging device that will allow you to backup at
whatever speed you need to, then move the data to tape at streaming
speed. (Note: Not all disk devices can stream data off of them fast
enough to stream these drives either.)

Example.  Let's say you've got 180 MB/s of backups.  You can:

Buy 4 LT0-4 tape drives and not stream them. 
(30 * 1.5:1 compression * 4 =~ 180 MB/s)

Or

Buy a disk array that can handle 180 MB/s and ONE LTO-4 tape drive to
copy your backups too when you're done with the backups.

There I feel better.

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