View Full Version : Max Raid on UL3D

11-19-2001, 08:16 PM
I am planning for a 15K cheetah-based raid for HD Video applications. I am wondering what is the number of 15K drives I need to have before I max out the 2 SCSI channels. My theory is that if I have 4 x 15K cheetahs on each bus that will give me 200MB/s per bus (the 15K data sheet says a min transfer rate of 50MB/s per drive). That means that the 160M bus will me maxed out.

So, theoretically if I add more drives, I will only add capacity, not speed.

Am I correct in these assumptions? The files will be very large video files.

Thanks .... taffy.c

11-20-2001, 10:16 AM

Back in early September someone posted numbers using UL3D and 2G X15 Cheetahs and found that two per channel was ideal. You may want to look at 36GB drive rather than 18GB?


11-20-2001, 10:54 AM
Hi Greg,
I built an array back in September with 2 x 36G Cheetahs on each of the 2 channels. It gave stunning performance (around 200MB/s on 8M+ file sizes). However, in order to support the sustained speeds of 10-bit High Def Video (around 170MB/s) across the whole array I want to go faster and to more drives.

Digital Voodoo, who make the HD Capture card I am planning to buy tell me that I need a minimum of 10 drives (5 on each channel) together with the UL3D. But I suspect that going past 8 drives will not add performance because the SCSI channels should be maxed out.The point of my original post was really to check what others think about this performance vs. drive count issue with 15K drives.

.... taffy.c

11-20-2001, 12:51 PM
Have you read this from ATTO?

ATTO Ultra320 (http://www.attotech.com/press/pressultra320.html)

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>a dual-channel host adapter utilizing the latest Ultra320 SCSI technology. Offering increased speeds of up to 320 MB/sec. per channel for a combined speed of up to 640 MB/sec.<HR></BLOCKQUOTE>

They're also moving into the ATA realm with another new product, "ATTO Technology's Diamond Series RAID Storage Arrays."


[This message has been edited by Gregory (edited 20 November 2001).]

11-20-2001, 01:31 PM
Wow! Thanks - that will be my new SCSI HBA for sure. Can the PCI bus of a current Mac actually handle 640MB/s? Seems like a lot of bytes/s.

.... taffy.c

11-20-2001, 04:29 PM
I may have this bass ackwards, but I was under the impression the U320 was a drive spec or instructions set, and that the U3LD would be supporting it as soon as drives drive (or perhaps via firmware upgrade).

As an aside, what is the theoretical PCI bus limit for you newer Mac users?

11-20-2001, 05:42 PM
They are calling this the UL4D - not just firmware. There is a photo and tiff image (http://www.attotech.com/scsihbaimages.html) on ATTO.


11-20-2001, 07:31 PM
Many many factors involved guys. The UL4D needs a 133MHz, 64-bit PCI bus (roughly 1 GB/s) to achieve its theoretical maximum throughput of 640 MB/s. A single PCI slot in the Quicksilver is limited to 215 MB/s throughput by design. I have seen folks post slightly higher numbers with 4x X15s on a UL3D but I assume the higher numbers are within the tolerance of measurement error and/or a gentle nudge of the envelope. The QS has a 33MHz, 64-bit PCI bus with a theoretical maximum throughput of 256 MB/s. From this, you can see that one UL3D and four X15s is just about as good as it gets. A second UL3d and some X15s hanging off of it would much more than max out the PCI bus.

11-22-2001, 02:03 PM
So, just to be clear, you are saying that going beyond 4 x X15 on a single UL3D in a QS mac will only add capacity - not speed?

Is apple planning to go to a 133M PCI bus in the future that we know of?


11-23-2001, 11:45 AM
Hey T.C.,

That is what I am saying. Actually (4) X15s might not get every last MB/s out of the PCI slot but it is so close that the cost of adding (2) more X15s just to oversaturate the card becomes nonsensical. You need to add the drives in pairs to this setup to maintain a balanced RAID array.

Anyway, 200+ MB/s reads and writes is pretty freakin' awful damn fast!!

You start to gain MB/s again when you add a second UL3D and begin hanging drives off of it but you will never get all of the 430 MB/s from two slots (215 x 2) because the PCI controller can only handle 256 MB/s. These are the upper limits of the performance envelope as it is now. I am sure Apple will one day have a 133MHz PCI bus but I don't look for it soon in this economic environment. Not a good time for expensive innovation (I'm sure 133MHz spec system components cost a ton more than 33 MHz spec components).