What's the relationship of OS X and SCSI?

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Hawaii Cruiser's picture
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I'm reading in places on the web that OS X and SCSI just basically don't get along very well. Is this true? Adaptec has abandoned SCSI support for OS X. It sounds like ATTO is still barely hanging in there, but is SCSI actually long since lost in the dust of OS X and SATA? Have those fast SCSI seek times become meaningless? Is the life of SCSI already over? And as far as OS X, was this apparent incompatibility with SCSI a result of the integral design of OS X, or just a calculated dump by a far-sighted Apple?

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FunnymanSE30's picture
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That's odd almost anything i

That's odd almost anything i plug into my lombard's scsi port that is an scsi device works fine with my OS X install.

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protocol6v's picture
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I have bought 4 Adaptec scsi

I have bought 4 Adaptec scsi cards at $300-$500 each and all of them no longer have support in OS X 10.4. Either the machine kernel panics or it just deadlocks. $1500 down the drain.

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SCSI and OS X

The last time I used SCSI with OS X was with my old beige G3's. Those were good times. Especially when I found that the 8gb partition limit did NOT apply to SCSI. After all, what else was I going to do with the 18gb scsi drive that I had. Though, that was 10.2 on those machines. I never really bothered with scsi on any version after that.

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Eudimorphodon's picture
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Re: What's the relationship of OS X and SCSI?

Hawaii Cruiser wrote:

And as far as OS X, was this apparent incompatibility with SCSI a result of the integral design of OS X, or just a calculated dump by a far-sighted Apple?

OS X has problems with SCSI because no one likes writing SCSI controller drivers for OS X. Ironically OS X itself *loves* SCSI, just not on a physcial level. Firewire, USB, SATA, and ATAPI IDE devices are all basically treated as if they were SCSI on a logical level.

Really, the truth is that SCSI, the parallel flavor, is dead as a physical medium. It's always been expensive, difficult to configure, and overengineered for consumer-level applications. Further, the basic concept of a shared bus for high-speed latency-sensitive devices like hard disks is becoming obsolete, in favor of point-to-point solutions which allow multiple drives to communicate with the controller (or multiple controllers) simultaniously without arbitration.

Read up on SAS, Serial Attached SCSI, which uses the same physcial medium on SATA and is backwards compatible with SATA drives, and you'll see how obsolete parallel SCSI is. Fiber Channel still has a future as well, but again, it's not really "SCSI" in the old Macintosh sense. With Parallel SCSI obsolete and overpriced for internal disk drives and USB-2 far more convenient and plenty fast for consumer peripherals like scanners and external disk drives there just really isn't a point anymore.

--Peace

Hawaii Cruiser's picture
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Kernel Panics

I've also got three Adaptec cards--a 29160 and two 29160N's--which I bought used off eBay auctions last year at an average of $25 each. I've also still got two old ATTO UL2D's which were once specially OEM for the B&W G3 but were never supported by ATTO after OS X showed up. I invested in a second bus of SCSI over the years mostly for my wife's video art hobby, and it suddenly dawned on me last night that maybe the main reason I encounter constant SCSI problems in OS X isn't because I've picked up faulty used equipment, but because it's just not possible to make SCSI truly compatible with X.

As for kernel panics, here's one of the webpages that stimulated my "ah-ha" moment last night. It has a possible workaround for the Adaptec cards:

Kernel Panic Workaround for Adaptec SCSI

protocol6v's picture
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I actually saw that page a fe

I actually saw that page a few days ago. It didn't work for me. I have a 29160, two 2940u2w, and a 2930cu. niether of the four worked with that "hack".

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Re: Kernel Panics

Hawaii Cruiser wrote:

two old ATTO UL2D's which were once specially OEM for the B&W G3 but were never supported by ATTO after OS X showed up.

I've got an AHA-2940U2B in the B&W Rev. 1 I recently picked up. So far 10.2 loves it, but I haven't tried 10.4 yet. I'm fairly certain that this is the original card for this 400MHz machine. It's listed with "9GB ULTRA2 SCSI" on the serial sticker. It came without a HDD so I put in a 'cuda 18XL 9.1GB (ST39236LW) drive. It feels about as fast as my 600MHz iBook, in basic usage. I'm sure the extra cache (1MB vs 512K) and the (substantially) faster HDD. I'm curious how 10.4 would run on it, but I need to find more compatible RAM and a better video card. The B&W doesn't like the high density DIMMs that my slot-load iMacs do, and the video card is the old 8MB ATi 3D card that came as an option in some old Beige G3MTs... I'm sure there is some graphics stuff that shows a difference, but for general web browsing the two are very similar.

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Support for all my SCSI card

Support for all my SCSI card was apparently dropped in 10.3. The last time my cards all worked was in 10.2 when i was using them with a DAT drive. I have thought about downgrading back to 10.2 but i would lose alot of features and security if i did so.

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Re: Kernel Panics

Hawaii Cruiser wrote:

I invested in a second bus of SCSI over the years mostly for my wife's video art hobby, and it suddenly dawned on me last night that maybe the main reason I encounter constant SCSI problems in OS X isn't because I've picked up faulty used equipment, but because it's just not possible to make SCSI truly compatible with X.

If Apple sold a SCSI adapter it'd work great. There's nothing fundimentally "incompatible" between X and SCSI. There are fundimental incompatibilities between X and third-party drivers, however. OS X from version 10.0->10.3 never had a really "stable" API for binary kernel extensions. (Function calls in one kernel version might have subtle undocumented changes that introduce incompatibilites with existing drivers and be very difficult to track down.) 10.4 introduced a new *supported* set of binary driver APIs which in theory might improve things in the future, but only if drivers are rewritten to use them. As you might of figured out, the SCSI controller manufacturers just don't care anymore.

It really is all about drivers, nothing fundamental about OS X.

--Peace

Hawaii Cruiser's picture
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Thanks Eudimorphodon, your po

Thanks Eudimorphodon, your posts are always so informative and detailed and straight to the heart.

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RE: What's the relationship of OS X and SCSI?

Been doing experiments with an old Adaptec 2940UW

10.4 has problems with the Adaptec78XXSCSI.kext
Nothing in ASP or DiskUtility

Replacing this with 10.3 or 10.2 version
ASP sees the card but DiskUtility cannot see the drive

I had heard that 10.2 was good with the card, but dropping 2 OS back just to use SCSI is a bit unrealistic.

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SCSI VS SATA/PATA etc

Personally I think this was a planned progression twards Better /
Faster / Cheaper. Along with the desire of Mac users to have many of the same options and integration with Windoze users.
And of course the frustration of SCSI card builders having to
rebuild there software for every new build of OSX.
I have always enjoyed the "feel" of a fast SCSI drive, I believe older users will know what I mean...
A great thread here
http://www.macgurus.com/forums/showthread.php?t=18063

Dave

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I am surprise to hear of thes

I am surprise to hear of these problems with SCSI and OS X.

I had a Gigabit G4 with a ATTO U2LD with a SCSI system drive. The thing ran like a champ. I ran OS X 10.3 and 10.4 on it no problem. The only issue I ever ran into is that if the PRAM ever got cleared it would take about 15min for the system to figure out where to boot. I wish I still had but I gave it to a friend that need a OS 9 system for his photorogphy hobby.

I am not surprised that Adaptec dumped OS X. IMHO they are very overrated.

Though I do agree that SCSI is on its way out. I have been out of the storage loop for a while, but from what I understand Serial Attached SCSI is awesome.

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Hawaii Cruiser's picture
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The truth is, I've run X off

The truth is, I've run X off my ATTO UL2D's and the card does seem to work fine. There's no X SCSI utility for it, though. I think some of the problems I've encountered are with the harddrives. A few nights ago I was experiencing video corruption while the UL2D was installed. After trying different things, I removed the UL2D and the corruption went away. Maybe it was just a glitch in the video card and a coincidence that the glitch went away when I removed the UL2D--don't know. I was planning to put the UL2D back in and see if it happens again, just haven't had the time yet. I've got a 29160N in there now and am experiencing no problems, but I don't have it hooked up to a harddrive. I'm just on ATA. But if anything, SCSI definitely does have more difficulty in X than I ever experienced in 9. This is all in my B&W.