PC Hardware

Tom · Guest

First off, let me apologize for the long post, but I want to give as
much detail as I can so that others can understand my setup and where
I may have some flaws in my understanding of the varieties of SCSI!

I'm trying to setup an external RAID using the following:

Mac G4 Quicksilver 933MHz
Running OS X.3 (using X's built-in RAID capability)
Adaptec 39160 U160 SCSI Controller
ALR 6-slot backplane (from Gateway ALR 8200 Server)
(6) Seagate Barracuda ST150176LC 7200 RPM 50GB LVD-80 Drives

I'm currently running into problems with the backplane (ie only
recognizing 1 drive) but I'm still trying to sort that out on my own.
Using a single drive and a 80 to 68 pin adapter for testing, I can get
around 20MB/s using Xbench. I bought these drives because of
capacity/price rather than speed, but I got a good deal on a 39160 and
would like to see how my system runs on faster drives. My main drive
currently is a IBM 120GXP on the Quicksilver's on-board ATA-66
controller and Xbench gives me read, write rates in the low 20's.

I've got about $250 invested in the SCSI drives, backplane, cables,
external power supply, case, and 39160. I know I probably could have
setup an ATA, SATA or Firewire solution cheaper, but 1) all these
items were not purchased at once, 2) I wanted an external drive(s)
that I could move to other computers, 3) this was my only Mac w/o SCSI
which was sometimes inconvienent, but now I've got it if I need it.

First some questions on LVD(Ultra2) vs U160 vs U320 SCSI:

1.) Will an LVD-80 drive give a better avg transfer rate on a U160
controller than an Ultra2 controller?
Or is this a physical property of the drive that will not change with
the controller interface as long as the controller max exceeds the max
transfer rate of the drive?

2.) Say a theoretical U320 drive had a avg write speed of 60MB/s and a
max of 120MB/s. Since this is below the maximum speed of a U160
controller, would the drive perform equally well on a U160 as on a
U320?

2.5) Am I correct that the basis for a U160 drive performing slower
on a Ultra2/LVD controller is the fact that the controller cuts off
the max transfer rates at 80MB/s thereby lowering the average speed
the drive can obtain? #2 may be an invalid question...do all U320
drives support a max rate of 320MB/s? Maybe that's why they're U320
drives....

3.) Gateway tells me the backplane I'm using supports up to LVD-80
drives. I'm under the impression that I could still use U160/U320
drives on this provided the answer to #2 is Yes (but in this case the
max speed of the drive would have to be under 80MB/s). Does this mean
the COMBINED max transfer rate of all 6 drives is limited to 80MB/s?

4.) This backplane can be split into 6x1 channel, 3x2 or 2x3. Assume
the backplane limits the max transfer rate to 80MB/s and 6 drives are
attached that can deliver a combined max rate of 120MB/s. That
throughput wouldn't be seen when the backplane was set to use all 6
drives on a single channel. However, would 120MB/s max be possible if
the backplane was split into 3x2 channels, with each delivering 60MB/s
max? Since a U160 controller would be able to handle the max rate of
120MB/s, would daisy-chaining the two 3 drive setups deliver 120MB/s
on a single channel? In the case of the backplane I've got, the dip
switches could be set to 3x2 and the termination between the two sets
can be seperately turned off, though I don't know if that would
function.

The above are just things I've been wondering about and a way to check
that my understanding of these standards and the logic behind my ideas
is correct. I understand the difference between theoretical max
transfer rates and the actual avg rates seen - but I may have
contridicted myself above.

Mac Specific Questions:

I'd like to get these SCSI drives working simply to learn what I'm
doing - and because I've spent alot of time reading up on this and I
did pay for all the stuff already! :) But I don't really expect super
fast perfomance out of this array. Which is fine, I don't need it.
But I'd like to see what I can do to speed up the system disk-wise.

Oh and is there anythings else (freeware) I should be using instead of
Xbench (besides things like doing large file duplication tests)?

Ideas:

- Add an ATA133 card. I hadn't realized the Quicksilver was all the
way back at ATA66.
- Add a second IBM 120GXP and use OS X software RAID
- Both the ATA133 card and the 120GXP using OS X RAID
- Hardware RAID ATA133 and the 120GXP
- If I were to go the SATA route, that would mean a controller and two
new drives. I hear some multichannel ( >2) Mac SATA controllers will
be coming out, anyone have any info on these?

And since this is the SCSI group I don't want to get too far off topic
with the above stuff. Since I'm more curious about speed than in need
of space, I've considered going with a few smaller 10K or 15K SCSI
drives.

- I'd like to go with 4 36GB drives, possbily 4 18GB's to keep the
price a bit lower. Two drives on each channel of the 39160 should do
pretty well.

- I don't think I'd trust that many high speed drives inside the G4.
And unless I can find a reasonably priced external enclosue with an
SCA backplane I want to use 68-pin dirves. I had difficulty finding
something for the Barracuda SCA drives, but that was mainly because
they're 1.6". Maybe my choices won't be so limited with 1" SCA
drives.

- Is there anywhere I can find info on older Maxtor/Quantum Atlas
drives and Seagate Cheetahs??? I know the current versions will be
the best, I don't know if older versions would be just as good for my
purpose. Prices on Ebay are all over the place so they can't be used
as any kind of performance indicator. Recommendations on particular
models would be great, or warnings on those to avoid.

Ok guys, sorry for the long post, but hopefully answers to my
questions won't take much more than a yes or no.

Tom

Questions on LVD, U160, U320 Mac SCSI RAID vs. ATA, SATA (Lo

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