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Date:	Fri, 29 Aug 2003 23:47:35 PDT7
From:	Steve Carter <scarter@vcnet.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: What SCSI adapter to choose !?

Content Type: text/plain

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Svobi:

Dual channel SCSI host adapters make a LOT of sense for backwards
compatibility reasons. Although SCSI is both backwards and (somewhat)
forward compatible, the HA will operate the bus at the lowest common
denominator (speed) of whatever is on the bus.

So, ...

using a dual bus host adapter, you can separate the old, slow, SCSI devices,
i.e. ZIP, MO, CD-ROM, and scanner from the newer faster, hard drives. ALL
LVD (low voltage differential) adapters will revert to single-ended if even
one device on a bus is single-ended, so a dual U160 HA can run one of its
buses as SE for our older legacy devices. External devices, e.g. scanners,
often have long cables which further compounds the speed problem with SE SCSI.
External cables, with their multiple connector interfaces, do not preserve
the bus impedance very well and SCSI bus data fidelity can suffer at the
higher bus speeds of FAST and Ultra SCSI (SE).

For me, and many others, the best solution is a dual bus HA, separating
the old, slow and external legacy (SE) devices from my (more) modern
Ultra 160 10Krpm (LVD) hard drive(s). The best physical design (inside/outside
the computer box) keeps the cable run as short as possible, and uses
active termination at the end of the cable. Using one bus dedicated to
legacy SE SCSI may limit the number of SE devices to 7, depending on
configuration. Most external devices, except hard drives, are SE.

Dual U160 HAs generally have two internal 68-pin LVD/SE connectors,
as do _EVERY_ONE_ of the HAs listed below, and a varying complement of
other connectors. Here are some HA choices I have been investigating.
There are others, but not of interest to me:

LSI Logic (dual channel, 30 devices max):
LSI 21040; one 50-pin internal header for legacy devices, 1x 68p external
64-bit PCI
LSI 21003; one 50-pin internal header for legacy devices, 1x 50p external
(this HA is hard to find) 32-bit PCI
LSI 22915A; two VHDCI external connectors, 64-bit PCI

Adaptec (dual bus, but not dual channel -- 15 devices max.):

AHA 29160; one SE bus and one U160 bus, but 15 devices total max.,
1x 68-pin U160 external. 64-bit PCI
AHA 29160N; one 50-pin bus (internal and external) and one internal U160
limited to 15 devices total, but _GREAT_ for legacy support.
($129 at scsi4me.com) 32-bit PCI
AHA 39160; 2x 68-pin VHDCI external, 1x 50-pin SE, 64-bit PCI

Tekram (uses LSI Logic SCSI chips, dual channel, 30 devices max):

DC-390U3D: 2x U160 LVD channels; 2x 68-pin VHDCI external,
1x 50-pin internal; 64-bit PCI
DC-390U3D: 1x U160 and 1x SE channel; 1x 68-pin external LVD, 1x 68-pin
internal SE, 1x 50-pin internal SE; 64-bit PCI

The retail Tekram packages come with a lot of cables and connector/adapters,
making them a good deal. Tekram.de announced a U320 SCSI HA, but it has
not yet appeared anywhere that I've seen -- status unknown.

If your motherboard doesn't have 64-bit PCI slots, you can still
use a 64-bit PCI card provided you have clearance for the additional
connector length. My AT MB is _SO_ old that this a problem and even
longer PCI cards don't fit. Modern ATX MBs should not be much
of a problem, but it's worthwhile to check first.

U320 dual HAs are also a good choice, but typically have _NO_ 50-pin/SE
legacy connector support. Not a problem if you're willing to use an adapter
and sort out the wide-to-narrow transitions in cabling and termination.
SCSI4ME.com is a good place to start shopping. eBay also has some good
prices, especially on the U160 LSI22915A for which you must use a
68-to-50 pin adapter and have room for an 8.5" long card.

Adaptec has a history of NOT providing drivers for their older HAs
and newer operating systems. There are no Window XP drivers from some
of the older Adaptec HAs, so they are readily available on the surplus
market for cheap. This is good news for OS/2 users who want an inexpensive
SCSI HA for their older devices. The OS/2 drivers haven't changed
and are available.

Still, my money will probably go to LSI Logic. They are the former NCR
Microelectronics folks and their HAs show up in SUN, HP, Compaq machines
and even have Linux drivers. There are OS/2 drivers at the u160 level too.
For U320, you probably have to go a recent (merged, v4.52) kernal to get/use
U320 drivers. Steven had a post recently about this. Upon reflection,
he's likely right.

--Steve (sorry for the length of this post... )

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
On 8/29/03, Svobi wrote, in part:
>I assume that it would be not bad to split in 2 different groups,
> i.e.
>Channel A: Scanner only
>Channel B: Data Storage
>
>At the moment I am not clear about using U160 in future !?
>But it could make a sense to split my present units into 2 groups,
> i.e
>Scanner and CD-ROM and
>HDD and MO drive !?
>....

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