View Full Version : 2 x 2940U2B + 2 Cheetah LVD in PTP/G3?

12-06-2001, 11:04 PM
Well, now that I've got my PTP/PowerForce G3 400 running smoothly thanks to the help I've received on this board, it's time to think about screwing it all up with an upgrade!

I'm running a three UW Cheetah RAID 0 though a OEM ATTO ExpressPCI UW card using SoftRAID 2.2.2 and getting 30-35mbs SR/SW with the ExpressPro-Tools 2.7 8mb bench. I want to do better that that, but I'm short on cash for upgrades right now (damned economy!) Here's what I'm thinking about:

Buying two 2940U2Bs from the Gurus, picking up a couple of Ultra2 or U160 Cheetahs or (I almost hate to say it) Atlas's and running a true two channel Ultra2 RAID taking advantage of the PTPs two pci busses. I have a very good local source for high quality cableing, and I already have SoftRAID, so this wouldn't be two big a financial hit to take for LVD RAID.

What kind of performance can I expect from such a setup? I'm trying to do a cost/benefits analysis. Would going for the U160 drives give me better perfomance through the 2940U2Bs than cheaper Ultra2 drives? Even though the U160s would be nice to have once I upgrade systems, if the Ultra2 drives are nearly as fast through the 2940U2Bs, I'll take the short term savings and wait for U320 to bring U160 prices down.

Thanks in advance for the help - Hap

12-07-2001, 06:21 AM
You'd be saving only $140 buying two 2940U2B rather than say ATTO UL3S. Shame they don't have a "board only" Miles2. Atlas 10k III are under $200 18GB and a close second to the X15's, and nearly half price to boot! IBM's Ultrastar 36LZX is $169. I'd just get a fourth drive, then go w/ ATTO UL3x later when you can do that.

When building a RAID you don't want to mix drives with different specs and quality cabling means only one thing: Granite.

Beware the bottomless pit of SCSI.

I find IBM's Ultrastar 36LZX to be "slow" but it gets ~29-34MB/s on its own on 2940U2B and they are U160 $169. If I put X15 on 2940U2B it does okay but even w/ RAID0 didn't get great SW. Atlas 10k III is right up in the 51MB/s.


12-07-2001, 08:56 AM

It has been well documented here in the forums that IF you have a 2 drive array it is slightly faster to keep them on the same channel. (Less scsi overhead or some such..) If adding a third or fourth then having 2 channels dramatically increaases speed.

I know that all the discussion on this has been using Macs with a single PCI bus (3 slots) though. having a 6 slot (2 bus) setup may give you a boost OR it could as easily involve more overhead and you would take a hit on this. I seem to know the ? but do not have the answer (sorry about that) But I thought you might need this info anyway.

Surely someone out there has done this? Anyone.....Anyone....Beuller?

12-07-2001, 02:41 PM
...just want to add that I bought and tried two 2940U2B's in B&W with one drive on each (Atlas 10k II's).

If you might be moving your array to a G4 or something, why invest in two year old technology? Also, the U2B is very very fussy about cabling and termination, and I just don't think you'll get the performance you might want.

A single X15 Cheetah ($339) and any U2 or U160 card is capable of 51MB/s, but could not "deliver" with two X15's. I'd rather see you buy one X15 and triple your performance.

12-07-2001, 03:34 PM
Ive got to agree with Gregory. Even if you have to do it piecemeal, get the good stuff. I put a UL3D in my G4 with a couple real old Cheetahs I had, when I get ahead on the bucks I'll move to a couple of X15s.(can't wait...at least not easily)

One fast drive/card is likely to cost about the same as a double dose of slow drives and SCSI cards AND CABLE$, and you'll probably get about the same performance with no possibilty of using them to upgrade in the future.

Make sure you account for future needs when you order cables, buying the darn things once is bad enough.


[This message has been edited by ricks (edited 07 December 2001).]

12-07-2001, 04:13 PM
I have tried a dual 2940U2B RAID setup in a PowerTower Pro with G3. I'm sorry to inform you it would not work in my particular setup, which had two video cards. After many long efforts at troubleshooting, I established that my PTPro would not boot under these conditions:

<LI> both 2940U2Bs installed, whether cables were attached or not.
<LI> two video cards were also installed, and one of them was an ATI.

If you have two non-ATI video cards, or only one video card, you can probably do a dual 2940U2B setup.

Also, it's possible that you could get it to work, even if you have two video cards (one being ATI), because your G3 daughtercard is a PowerForce. Mine is an XLR8, and I never tried booting it with the original 604e installed.

If you want to read more about what I went through with the dual 2940U2B experiment, read these two threads:
http://www.macgurus.com/ubb/Forum3/HTML/000369.html http://www.macgurus.com/ubb/Forum8/HTML/000206.html

Warning: they are long, meandering and exhaustive threads. I'll go ahead and tell you that the way I worked out the solution in the end was to replace one of the 2940U2Bs with a Miles2. Yes, I've been running a dual-bus RAID of two Cheetah 10Ks with one Adaptec controller and one Initio controller.

As for your other questions: I've never heard myself that a two-drive RAID is faster on one channel than two. That would suck since I went to a HUGE effort to make my system a dual-bus RAID with only two drives.

Good luck.

12-07-2001, 05:33 PM

A 2 drive single channel raid is just the tiniest bit slower than a dual channel 2 drive array but it seems to be the consensus here that the added MB or two isn't worth the added expense of the dual channel card and cables & Terms

See Kaye's post here

I earlier had said "slightly faster" for the single channel This was a late night brain cramp....

[This message has been edited by Damien (edited 07 December 2001).]

12-07-2001, 06:04 PM
One very important consideration is bus speed. The vintage Macs such as a PTP benefit greatly from the dual card arrangement or dual bus as magician calls it. I tried a bunch of configs with multiple X15s and one or two Miles2 cards which need to be in PCI slots 1,4. The New World Macs, different story.

With a vintage Mac and a single Miles2, adding X15s and striping, I could dramatically increase sustained read, but sustained write never went above 40+MB/s. I could do that with one X15. A bus limitation. Same with a dual channel UL3D card in the PTP and utilizing both channels. Sustained write stuck at 40+MB/s.

However with dual Miles2 and two or four or six X15s, the sustained write limit becomes history. It goes up like sustained read, where both reach a very much higher ceiling. Several of us have done this, users as well as moderators/rulers. The one catch most of us have found, you must enable Write-through. Running MacBench 5 or doing large file size transfers will cause a freeze. No damage but you must reboot. Enabling Write-through causes about a 7% decrease in CPU, 7% in FPU, 3% in Graphics and 3% in Pub Graphics because now you are routing everything thru the much slower main memory. Louie likes to call it a 20% hit. I don't disagree. Of course a G4 upgrade is already set for Write-through, but a G3 takes a performance hit. k

12-07-2001, 07:23 PM
Just spent the day trying to resolve an issue with 2940U2B in 7300: the GD cable connector on external just don't fit - so I put an ATTO UL3S in 7300 and saw nearly 30% degredation on what I was getting in B&W with same drive. The PCI slot and those GD connectors hit plastic plate and required more tork than I like. Little things I never expected to become issues. When someone here says Miles2 in Vintage I have a better understanding - and I thought I'd read everything ;(

So now I have two 2940U2B's in B&W and may get around to RAID and see what it can do (once I can get another X15 of course http://macgurus.com/infopop/emoticons/icon_wink.gif


12-10-2001, 02:59 AM
Thanks everybody for the help. It sounds like trying to cheap-out with the dual 2940U2B RAID in an attempt to get around the bus speed limitation of the PTP is not the best idea. I think I'll save my cash and invest in a single Miles2 and two to three drives and see what I can do with that. My goal was to save some cash AND take advantage of the two busses on the PTP, but I have to agree with the posts recommending buying quality, current technology the first time around. Thanks again for help, and I'll post my results when I get something going.

- Hap