ADSM-L

Re: LTO slow restore?

2002-08-23 06:23:27
Subject: Re: LTO slow restore?
From: Zlatko Krastev/ACIT <acit AT ATTGLOBAL DOT NET>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Fri, 23 Aug 2002 13:21:58 +0300
LTO is much slower when it becomes to single/small files compared to both
3590x and 9x40 drives. Start/stop times and acceleration of 3590/9x40 are
much better than for DLT/LTO. The latter have to rewing back to accelerate
at reading speed after tape positioning. Compare how much time takes to
read label (several bytes) after mount in different technologies.
There is no need to repeat all the arguments you got a week ago but think
of *class* of the drive:
- high-end (top performers) - both IBM and StorageTek give close results
with 3590B/E/H and 9840A/9840B/9940A respectively. Compare to very fast
Ferrari with only two seats. Price is as you can expect very high.
- mid-class (price/performance) - DLT/SDLT/LTO/AIT/Mamoth from many
vendors. Different vendor approaches with different results. Some focused
a bit more on capacity (LTO/SDLT), others focus on mount times (AIT), but
always acceptable priced. Think of it as a van/pick-up/limo/sedan/etc.
- low-end (price only) - DDS/Travan. Price is main concern (last year fell
down about 50%), some capacity + some speed (20 GB @ 5MB/s for DDS-4),
both lower than for mid-class. Think as for VW Beetle or any small
Japanese car for in-city use.
So you try to compare (top performer in) mid-class to high-end old (3590B)
and new technology (9940A).

Both Porsche and Cadillac can reach 200+ km/h but for 11 and 35 seconds
respectively (last numbers might be inaccurate but the ratio is close).
Driving on straight desert road both cars can take 100 km for about half
hour. But in the mountain with its fast acceleration and better brakes
Porsche will sure overtake the Caddi.
And now the question in front of you is what to buy in place of good old
Chevy Corvette:
- replace with Grand Cherokee because you are no more at 20 and needs have
changed
- buy a Viper trading back the Chevy for better price
- go and buy Ferrari/Mazerati
Do not compare apples with oranges.

Zlatko Krastev
IT consultant




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Subject:        LTO slow restore?

Hello,

I am trying to understand why LTO is so much slower than 9840B or 9940A
when restoring a file?  I know that it takes longer to load the tape and
the performance is slightly slower, but what is the technical reason for
LTO having slow restores for files and databases?  Does anyone have any
statistics/numbers that I might be able to go by?  Right now we have
3590's
and we are getting about 25 GB/HR on the mainframe.  We are going to be
moving TSM to a SUN/Solaris server which will be put on the SAN.  Mainly I
am trying to understand what goes on when a server tries to restore a
file/database from an LTO tape and how the 9840B or 9940A is better?
Thanks in advance for any input!!!!

Joni Moyer
Associate Systems Programmer
joni.moyer AT highmark DOT com
(717)975-8338

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