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Four Drive RAID on the G5:
Ultra 320 SCSI vs
Serial ATA vs FireWire 800

Originally posted 12/05/03 by rob-ART morgan, mad scientist
Updated 01/30/04 with Ultra320 SCSI RAID numbers.

HYPOTHESIS: If you have one channel per drive, a FOUR drive striped array (RAID 0), either FireWire 800 or Serial ATA should produce sustained READ and WRITE speeds approaching 200MB/s.

Why does one need such speed? Many digital video editing labs are trying to capture HDTV format uncompressed. Depending on the frame rate and resolution, you need write speeds of at least 120MB/s and as high as 180MB/s.

Why not just use Ultra320 SCSI arrays -- aren't they faster? They are historically faster, but are expensive and the drive capacity is one-third that of most contemporary SATA and PATA drives.

Based on the theoretical speed of FW800 and SATA, using the fastest available drives and multiple channels should produce the desired performance at a fraction of the cost.


As expected, Ultra 320 dual channel SCSI mated with four 15,000 rpm drives is faster than quad channel Serial ATA and FireWire 800 RAID. But it will cost you three times as much and you'll end up with one-third the total capacity.

Last November we discovered a problem with multi-channel FireWire 800 RAID on the G5. The sustained WRITE speed was much lower than SATA... AND... much lower than a Dual G4/1.42 Power Mac with the same configuration (see second graph above).

I've asked around as to why the G5 could only achieve sustained WRITE speeds half that of the G4. Nobody has any hard answers. Only theories. Some blame Apple's PCI-X controllers. Some think it's a G5 firmware bug. Some think it's a deficiency in the PCI controllers or an incompatibility between those controllers and the G5's PCI-X slots.

Two of my colleagues in two other labs with similar setups observed the same phenomenon. We tried different drives, different case kits, and different PCI controllers -- same result. We even tried putting one FW800 card in slot 4 (133Mhz) and one card in slot 3 or 2 (100MHz - different bus) -- same result.

I'm hoping Apple engineers can help solve this mystery since I've passed my findings on to them. I hope it's a simple firmware fix or OS patch -- and doesn't require a Rev B motherboard!

Multi-channel Serial ATA RAID has definite promise. It exceeded the goal of 200MB/s.

One caution, however. If you are using more than one SATA PCI card on a dual G5, your speed will be affected by what PCI-X slot combination you use:
Slots 4 and 3 = 230MB/s READ, 225MB/s WRITE
Slots 4 and 2 = 230MB/s READ, 225MB/s WRITE
Slots 2 and 3 = 178MB/s READ, 56MB/s WRITE

Some of you corrected me by saying there can't be a "Slot 4" since there are only 3 PCI-X slots in a G5. But Apple designates the AGP slot as slot #1. Then it labels the two PCI-X/100 slots at #2 and #3. The one PCI-X/133 slot is slot #4. (System Profiler confirms this when you click on "PCI/AGP Cards.")

What happens to speed as the drives fill up?
When I tested the "END" or inner tracks (90% full) of the SATA array, we measured half the speed as the outer tracks. If you plan to fill up your drives, you may find the performance toward the end unacceptable. The lowest quality uncompressed HDTV footage requires 120MB/s sustained write speed (see graph below).

We had a brainstorm, though. If you are comparing the speed of the inner tracks of a SATA RAID with that of a SCSI RAID, you must take into account that the SCSI RAID capacity is less than one-third of the SATA RAID. When we measured the speed of the SATA RAID 30% mark (which is equal in capacity to 90% on SCSI RAID). The SATA RAID was FASTER! And at the 60% mark, the SATA RAID could still WRITE faster than 180MB/s after capturing twice a much as the SCSI RAID or a total of 559 gigabytes!

SUGGESTION: If you need to maintain 180MB/s during HDTV uncompressed capture, use SoftRAID 3.02 to partition the RAID set so that the last one-third (slower section) of the RAID volume isn't used for capture.

WHAT IS DISKTESTER? It is a disk speed testing utility by Lloyd Chambers that must be invoked via the Terminal app. It allows you to set parameters like test file size (1024MB), system cache (on/off), iterations, starting block size, etc. My favorite option is the one that lets you reserve a contiguous block which can be tested in predefined segments. I used it to divide a newly formatted RAID set into 10 parts so I could plot the falling transfer rate as the inner tracks were approached. That method is much faster than utilities that test the entire drive like Winbench and SmartVue. For more info, visit Lloyd's Software Tools page.

Check with Wiebetech. They have a product called G5Jam that puts a 3rd and 4th SATA drive inside the G5.

If you want an external SATA RAID box, ProMax is offering both a two and four drive setup.

If you don't mind putting the SATA drives in individual boxes, you can buy SATA enclosures from Frys Electronics for as little as $50.

WHAT IS A SeriTek/1S2 AND 6890M? In order to add two more SATA channels to the two that come standard on the G5, I installed a SATA PCI host adapter. The two cards available are the FirmTek SeriTek/1S2 and the Acard 6890M. (There may seem to be others but they are derivative of those two.)

As you see in the above graphs, the FirmTek SeriTek/1S2 was the best performer. The graphs below further illustrate the variations in performance with dual drive RAID 0:

Not only was the SeriTek/1S2 faster than the 6890M, the price was much lower ($70 vs $159). You can buy two SeriTeks for the price of one 6890M. The SeriTek/1S2 works on all Macs with PCI slots.

The 6890M did have one unique feature: The ability to create a RAID pair at the card level using micro switches. Why is that cool? Because the OS thinks it's a single drive, allowing you to PARTITION it using Apple Drive Utility, reserving the fastest portion of the drive for speed critical applications.

Another advantage of the SATA solution or FireWire 800: it DOES support Deep Sleep. FireWire 800 PCI host adapters do NOT support Deep Sleep at this time.

The newest model of WD Raptor 10K SATA drive was clocked at 72MB/s by Storage Review. And it clocked 54MB/s at the slower inner tracks! That implies that four of them could well exceed 200Mb/s even when full... but full means about 280GB total.

SoftRAID versus Apple Disk Utility in terms of speed. And features compared.


Our Hitachi 7K250 Serial ATA drives and ATA-100 drives (for FireWire 800 cases) were provided courtesy of Trans International. Be sure to check their site for pricing. Check also with Other World Computing.

The best performing Serial ATA PCI host adapter was the $69.95 SeriTek/1S2 provided to us by FirmTek. This card works on all Macs with PCI or PCI-X slots. It is available direct from FirmTek's online store for $69.95. Check also with Other World Computing and Trans International. Sonnet Technology will sell you a purple version (Tempo Serial ATA) for $99.95.

The 6890M SATA RAID host adapter for the Mac was provided by Acard. It lists for $159 on Acard's online store. It's also available from their distributors and dealers.

How do you add more SATA drives to a G5 when it only has two bays? Wiebetech has a product called G5Jam that puts a 3rd and 4th SATA drive inside the G5.

If you want an external SATA RAID box, ProMax is offering both a two and four drive setup.

Our FireWire 800 cases and PCI host adapters were provided by Wiebetech and FWDepot. Before you buy, check also at Other World Computing, Trans Internatinal, and Granite Digital.

If you have an ATA-100 or ATA-133 drive you wish to convert to a SATA drive, you might take a look at the $120 SATA Dock from Wiebetech or the $25 SeriTek/1SC1 PATA to SATA adapter from FirmTek. My testing shows there is no performance loss in the "translation."

If you choose to go with SCSI on your G5 (or G4), I recommend the ATTO Tech UL4D controller, Seagate Cheetah 15K.3 73GB drives (ZipZoomFly), and Cases/Cables from Granite Digital. Expect to pay at least $3000 for a four drive setup.

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2003-2004 Rob Art Morgan
"BARE facts on Macintosh speed FEATS"
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