When I first started using the 3590 with ADSM I had much of the same
concerns as you have highlighted here. I am running ADSM on a RS6000 AIX
box and am using the API to communicate with ADSM from within my
applications. At one point I was sufficiently unhappy with ADSM's
performance (I have made changes since that have improved things
dramatically) that I started writing my own manager directly to the 3590
tape driver. This worked quite well, but I can't replace the 1000s of
person months put into ADSM within a few weeks and as such I scrapped the
idea once I found better ways to use the ADSM API.
I did find that the 3590 is a great performer as far as tape devices go.
When talking directly to tape, I was able to randomly retrieve 100KB files
off a 10GB tape with reasonable performance. If I was careful how I sorted
files before reading them, I could achieve consistently good performance.
The trick was I needed to be aware of the way in which the 3590 writes to
tape. The following docs helped significantly:
IBM SCSI Tape Drive , Medium Changer and Library Device Drivers -
Installation and User's guide. (GC35-0154-01)
Magstar and IBM 3590 High performance Tape SubSystem Technical Guide (Red
Book GC24-2506-00)
From my experimenting, I am fairly sure that ADSM does not make the best use
of the 3590 capabilities, nor the dual gripper feature of the 3494
Library... I had heard (some time ago) that IBM was focusing on performance
issues including the 3590 in their next release... Perhaps some release
insight would help here...
At 10:28 AM 7/10/96 -0400, you wrote:
> I'm seeking insights into just how data is accessed within a 3590 tape,
>and more specifically, how ADSM accesses it.
> We currently have an AIX system with a client and server on that same
>host, with fast/wide SCSI connections to 3590 tape drives in a 3494 tape
>robot. All data (some 10 GB) is currently contained on one 3590 tape.
>We find that in retrieving an HSM-managed file (small) which has been migrated
>to tape that it takes a nominal 3 minutes to get the file back to disk, that
>time including the 32 seconds that it takes for the tape mount to complete.
> More recently we had an experience where we needed to retrieve a bunch of
>files, averaging 1MB in size, to copy to a non-ADSM 8mm tape. All of this
>data is on a single 3590 tape, as stored by ADSM, and in total is some 1.5GB.
>We started that job yesterday and, some 22 hours later, it is less than half
>done. The 3590 tape has remained mounted all the time.
> It's obvious that tape, be it 3590 or any other kind, makes a poor random
>access medium. We just didn't expect it to be this bad - almost
>debilitatingly bad. These experiences beg some questions which someone may
>have answers to...
>
>1. Just how does data access occur on a 3590 tape?
> The usual 3590 manuals go no further than quoting specs (128 data tracks on
> a tape, accessed 16 at a time, making for 8 pathways; plus servo tracks;
> etc.). Does anyone know of a written description, preferably available
> online, which delves into the mechanics of going after data on a 3590?
> (Can a host program, for example, take a shortcut to one of the pathways
> rather than plow through the whole tape to get to a given file. Is there
> any kind of direct addressability on 3590s? Etc.)
>2. Just how does ADSM manage data on 3590 tapes?
> I can find no information on this. Does ADSM store database information as
> to where on a tape a given file lives, or is it limited to knowing that
> it's somewhere on a given tape?
>3. Is there a way to get from ADSM a list of the files as they are stored on
> the tape?
> If we could get this we could go after the files in the order in which they
> appear on the tape and make retrieval sequential instead of random, thus
> dramatically reducing retrieval time (and drive monopolization and tape
> head wear, etc.).
>
> Any information in these areas would be appreciated.
> Richard Sims, Boston University OIT
>
>
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Chris Hopkins cjhopkin AT on.bell DOT ca
Chris Hopkins cjhopkin AT on.bell DOT ca
Sr. System Designer
Highway 407 Electronic Toll Collection System
Bell Sygma Telecom Solutions
Toronto: (416) 215-2910
Ottawa: (613) 781-4544
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