>>>>> "Curtis" == Curtis Preston <cpreston AT glasshouse DOT com> writes:
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).
Curtis> Lies. LTO-4's minimum speed is the same as LTO-3's, just
Curtis> under 30 MB/s. And, remember, this isn't an infinitely
Curtis> variable speed. It's 30, then 50, then 100, or something like
Curtis> that. If you're going faster than 30, it's going to go 50,
Curtis> etc. This means you'll rarely truly match the speed of your
Curtis> drive.
Heh, it's good to know that they all lie. Don't you just love sales
people?
>> 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.
Curtis> Don't believe it. Whoever said that is out right lying. If
Curtis> that were the case, they would be shouting this from the roof
Curtis> tops.
I didn't believe him either, and I'm sure the specs will bear it out
even more, since I'm going to hunt down the LTO specs from both
vendors. What's worse is that it really makes them look foolish, and
of course you wonder what else is being shaded truthwise.
Curtis> I will say it again, this time in caps.
Curtis> IF YOU ARE BACKING UP TO A TAPE DRIVE AND NOT USING IT TO ITS
Curtis> FULLEST RATED SPEED, YOU ARE WASTING YOUR MONEY. I have
Curtis> people that are using tape to its fullest, but at speeds over
Curtis> 100 MB/s, it's really hard to do so directly, and EXTREMELY
Curtis> hard to do so when backing up across the network -- and you'll
Curtis> be using insane multiplexing settings to do it.
I agree here 100%! Basically, with today's setups, D2D2T is really
the only way to go to get the performance, and reliability and density
of tape use.
Curtis> If you want your primary repository of backups to be tape, at
Curtis> least buy a properly designed disk staging device that will
Curtis> allow you to backup at whatever speed you need to, then move
Curtis> the data to tape at streaming speed. (Note: Not all disk
Curtis> devices can stream data off of them fast enough to stream
Curtis> these drives either.)
I keep asking vendors about the PCI bus bandwidth and how do they
think a single gigabit ethernet port can handle two LTO-4 tapes drives
running at full speed?
Curtis> Example. Let's say you've got 180 MB/s of backups. You can:
Curtis> Buy 4 LT0-4 tape drives and not stream them.
Curtis> (30 * 1.5:1 compression * 4 =~ 180 MB/s)
Curtis> Or
Curtis> Buy a disk array that can handle 180 MB/s and ONE LTO-4 tape
Curtis> drive to copy your backups too when you're done with the
Curtis> backups.
Heck, I'd get two drives if only for the redundancy when one breaks,
but stream to each drive one at a time if I can't feed them both at
speed. No real disagreement here, just belt and suspenders thinking.
Curtis> There I feel better.
There there, we can get you therapy. :]
John
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