Re: SCSI Hard Drive Questions
Oz Dror <dror@earthlink.net> writes:
| I have two systems one with 2940UW and seagate UW drive pentium
| 200MMX 128MB RAM
|
| the second with aic7890 (which is like the 2940u2w) and a seagate u2w drive
| pentium-II 400Mhz 256 MB ram
|
|
| the second system clearly runs faster. disc access is faster, it
| boots faster it takes about 4 minutes to compile the kernel vs 8
| minutes on the old system
|
| Disc access in the second system is 80M/sec v.s. 40M/sec.
|
| I am sure that the increase in performance is in part due to the
| u2w.
I don't think that's the case (see below).
| -Oz
|
| PS: the price of the new system is about $700 more than top of the line IDE
| system.
I wouldn't consider this a fair comparison. Obviously the processor
speed being at least twice as fast on the second system heavily
weights the results. In fact, I think that's ALL you're seeing when it
comes to kernel compilation.
The important thing to remember is that there isn't a *single* disk on
the market that even comes close to saturating the 40MB/s available on
a UW bus. The only time you see the benefit of the 80MB/s available on
a U2W system is when you have multiple devices accessing the SCSI bus
simultaneously, the most prominent example being RAID devices. You MAY
see some of that 80MB/s if the drive has a built in cache, but the
cache on most drives is so small I don't think it'd be a significant
factor.
In addition, in order to get that 80MB/s you have to keep the bus pure
U2W, i.e., you can't connect any UW, U or SCSI(1|2) devices to the
same bus or it automatically reverts to the 40MB/s Ultrawide
mode. Today that means, pretty much, the only thing you can use your
U2W adapter for, and get the 80MB/s performance, is hard drives. Other
than hard drives, as far as I know, there isn't a wide selection of
U2W devices available on the market. Certainly not at comparable
prices.
Of course there are other advantages to a U2W LVD system. If you keep
all LVD devices on the bus you don't have the almost ridiculous
limitations on cable lengths associated with a UW bus. Of course,
again, to see this benefit you have to keep the bus pure U2W, and keep
other devices on a different SCSI bus.
Personally, I wouldn't spend the extra $$ on a U2W controller for my
PC. For a server it might be a different story. Or if I had money to
burn! :)
And if you do decide to go with just UW, take a look at the Mylex SCSI
adapters. They're generally cheaper than Adaptec and I've seen reports
of better performance. Plus, while Adaptec just recently started
actively supporting Linux, Mylex (used to be Buslogic) has supported
Linux from the beginning, being very open with the programming specs
for their adapters. Don't get me wrong, I myself have a 2940UW, but if
I knew then what I know now I probably would've gone with
Mylex. Shoot, I think they even have a U2W adapter now so if you
decide to go that route it might be worth a look.
Good Luck,
Gary
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