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Originally posted 12/05/03 by rob-ART
morgan,
mad scientist 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.
CONCLUSIONS 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). 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: 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? 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. WHERE DO YOU
PUT THE THIRD AND FOURTH SATA DRIVES ON A 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. DEEP
SLEEP? LINKS OF
INTEREST SoftRAID
versus Apple Disk
Utility
in terms of speed. And features
compared. WHERE TO
BUY 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. Has Bare Feats helped you? |
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© 2003-2004 Rob Art Morgan "BARE facts on Macintosh speed FEATS" Email webmaster at rob-art@barefeats.com |
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