ADSM-L

Re: ADSM IO-Performance Tuning Tips welcome !!!

1997-10-30 16:16:47
Subject: Re: ADSM IO-Performance Tuning Tips welcome !!!
From: Steven P Roder <tkssteve AT ACSU.BUFFALO DOT EDU>
Date: Thu, 30 Oct 1997 16:16:47 -0500
> and we see, that ADSM doesn't use all the speed of hardware.
> We have an SSA-Subsystem and DLT7000 drives and we dont get the expected
> I/O rates with ADSM.
> Our DLT7000 drives perform with about 10-12 GB/hour with compression
> enabled
> (write speed is 5 MB/sec. w.o. compression so we should get at least 18
> GB/hour).
> The same effects we see with our SSA-Disks.
> They'll never perform over 4MB/sec and in middle with 2.5 -3.5 MB/sec with
> ADSM
> and no other I/Os are running on that machine.
> In an native environment(cp,dd,...) we get better device rating's with the
> same devices,
> so its our opinion,that it's a problem with ADSM.
> Maybe this is the way,how ADSM works , but I'm interested in other
> Benchmark Data
> with adequate devices .

I had/have some DLT7000's which I have had tons of problems with.  Quantum
came out, and attached an analyzer to the drives to capture the failures I
was seeing.  At that time, they commented to me about ADSM's start/stop
nature of utilizing the drives, and openly wondered if that may have been
the problem.  The DLT7000's are optimized for applications that stream
data.  In fact, the drives will automatically drop out of compression if
the data does not come fast enough, and this is what mine did.  Therefore,
I am only seeing native capacities on the tapes.  One can force this
option to "max capacity mode", and I would recommed that in an ADSM
environment if you want to maximize capacity.  In short, you will never
see the advertised thruput on DLT7000's under ADSM.  The IBM 3570
MagstarMP drives, on the other hand, are optimized for start/stop
performance, and although they advertise data rates of 2.2MB/sec native,
they out-perform DLT7000's in a start/stop environment.

The outcome of all this here is that we are returning the DLT7000's, and
going with the MagstarMP drives in a 3575 library.

Steve (unVMix Systems Programmer/Dude) Roder
(tkssteve AT ubvm.cc.buffalo DOT edu | tkssteve AT acsu.buffalo DOT edu | 
(716)645-3564 ,
   | http://ubvm.cc.buffalo.edu/~tkssteve)
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