Actual observed transfer rate here is 15 MB/sec per drive, two drives on the
same card. These are feature code 6205 dual SCSI-II cards in an IBM S7A,
with just one port in use. I feel I'm being limited by the SCSI cards,
because this application is showing a 3:1 compression ratio on tape and
should be seeing something along the lines of 35 to 45 MB/sec if IBM's
write-up on the LTO can be believed. (I get between 245 and 342 MB of data
on the 95 GB LTO tape). I hope to get some additional 12 meter cables after
the first of the year and see if I can get better performance by using both
ports on the card.

OTOH, I may be running into internal limitations on the PCI bus from the S7A
-- the cards are in slots listed in the PCI Adapter Placement reference, but
in the seventh and beyond listed slots (the more preferred slots having
in the seventh and beyond listed slots (the more preferred slots having
fiber channel and gigabit ethernet cards).

Depending on the system you're driving the tapes from, you may hit a
bottleneck at the system bus level before you hit the SCSI-II bottleneck.

Tom Kauffman
NIBCO, Inc

> -----Original Message-----
> From: Cook, Dwight E (SAIC) [mailto:cookde AT BP DOT COM]
> Sent: Thursday, December 20, 2001 10:56 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: SCSI Channel to LTO drive rule of thumb
>
>
> Well, I can fill you in on 3590 drives and that might be
> close to LTO's
>
> for each drive on the chain, add half of the previous drives thruput
>
> with 3590-B1A's a single drive on a scsi card all by itself
> is rated at 9
> MB/sec
> add another one on the chain, you will gain another 4.5
> MB/sec  (9/2)  or a
> total of 13.5 MB/sec
> add another one on the chain, you will gain another 2.25
> MB/sec   (4.5/2) or
> a total of 15.75 MB/sec
> add another one on the chain, you will gain another 1.125
> MB/sec   (2.25/2)
> or a total of  16.875 MB/sec
>
> so you see, past two drives on a card, things get ugly fast...
>
>
>
> -----Original Message-----
> From: Taylor, David [mailto:DTaylor AT WBMI DOT COM]
> Sent: Thursday, December 20, 2001 9:21 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: SCSI Channel to LTO drive rule of thumb
>
>
> Hi *,
>
> Can anyone share with me, a good rule-of-thumb for the
> maximum number of LTO
> drives that should be attached to a single Ultra-II SCSI bus?
>   Using the
> theoretical max transfer rates of 15 MB/s for the drives and
> 80 MB/s for the
> SCSI, I shoould be able to put 5 drives on one bus and still
> have room to
> spare (theoretically).    What is the generally accepted
> maximum number, in
> the real world?
>
> TIA
>
> David Taylor
>
>
>
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