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From: salem@hauk.hsr.no (Salem, Lazaro)
Newsgroups: comp.os.386bsd.questions
Subject: Re: SCSI or IDE HD?
Date: Thu, 11 Aug 1994 13:35:44 GMT
Organization: Rogaland University Centre
Lines: 226
Message-ID: <salem.147.776612144@hauk.hsr.no>
References: <salem.137.2E48D259@hauk.hsr.no> <graphix.776531255@spiff.cc.iastate.edu>
NNTP-Posting-Host: pc-salem.hsr.no
In article <graphix.776531255@spiff.cc.iastate.edu> graphix@iastate.edu (Kent A Vander Velden) writes:
>SCASI?
Ok. sorry for ofending you with my ignorance, but you'll have
to get used to it for a while till I learn how to call things
by their names.
I wrote:
> I bought a PC-clone,i486/DX33 Mhz, with 16Mb RAM (70 ns),
256 Kb cache, ISA bus + 2 VL-bus and
> -----> a SCSI host Adapter (ADAPTEC 1542CF),
> -----> 2 IDE HD controllers
yes... I said 2=TWO IDE controllers so I could install up to 4 IDE
HD!)
> But.. I haven't buy the Hard Disk yet and I was considering buying
> a Quantum 420Mb.
> I am not sure about the convenience or not of buying a SCSI or an IDE
> disk. I can get any of them at the same price (almost), and since
> I have both IDE and SCSI controllers already,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> I wonder what other considerations shoud I take to make my mind.
> As far as I understood (was told) there would not be any sensible
> difference for a one or two HD stations ("the botleneck is the bus
> speed" they said).
> I plan to have both 386BSD (on the 1st partition) and DOS on
> the 2nd partition.
Let me add this one:
Does 386BSD (DOS) like SCSI (IDE) better than IDE (SCSI)
or the performance is indiferent to the operating system I use?
> Any suggestion? Technical answers welcome.
^^^^^^^^^^^^^^^^^^^^^^^^^^
1) John Dyson <dysonj@delphi.com> writes:
> Go with SCSI -- I am stuck in IDE land right now, and there ARE
> advantages to using a busmastering SCSI interface as opposed to
> a programmed I/O IDE interface (Performance.)
Then <james@hermes.cybernetics.net> (James Robinson) writes:
> I'll agree, and I doubt that you will find anyone that says otherwise. If
> you do not mind the initial extra cost overhead (drives cost a bit more,
> and the controller costs quite a bit more than an IDE controller),
I already have both adapters and get both drives at almost the same price,
so is no a cost question but a performance one.
> you would really be doing yourself a favor by going SCSI. Less "BIOS
> translation" worries, _much_ better response / CPU loading via
> bus-mastering DMA,
> etc.
^^^? (mind to specify?)
> Plus, you can chain up to 7 devices off of your one SCSI controller.
I know, but as I said, I already have the IDE (times 2) and the SCSI.
The question is performance. [keep reading ;-) ]
> 7gig drives (not gonna happen w/IDE-current. Anyone know about the new
> IDE specs?),
Eventhough it is not the solution I am thinking of, here it is. You
(James) can read about Enhanced IDE (EIDE) in the article "IDE takes
off", BYTE March 1994. I quote some of it:
"...Type B DMA offers a transfer rate of 4 Mbps, while Type F ,
supported by PCI local bus, extends this to either 6.67 or 8.33 Mbps,
depending on the PCI/ISA bridge chip set in the system (both Type B and
Type F DMA requires BIOS changes)."
....
"In addition to extending the # of devices IDE can support, enhanced IDE
also extends the type of devices. .... Western Digital proposal for
supporting CD-ROM is called ATAPI (ATA Packet Interface) (NB: IDE=ATA)
... at it can be easily adapted to other devices such as a tape."
"Focused on the mainstream, EIDE represents an excellent low-cost
solution for most users and offers significant performance improvement
over std IDE. The fact that it is low-cost doesn't mean that this
solution doesn't offer significant performance improvement over std
IDE; it does. But it also offers a no-hassle peripheral-connection
method that everyone can like."
I repeat that this reflect not my my opinion and it won't be my
solution!. Please, let us no argue about that article.
> SCSI CDROM drives, scanners, tape backups, etc. Just the
> other day I grabbed the external SCSI 4mm DAT tape backup unit we have
> lying aroud work and backed up my paltry 340 meg maxtor. Just hooked it
> up and ran tar. Had I not gone SCSI, I would have had to have opened
> up the case to plug in some sort of floppy drive controller hosted tape
> backup unit (which we don't have lying around).
You mean, eventhough I have 2 IDE controllers AND the SCSI adapter,
it would be much difficult to make backups of and IDE drive than of
a SCSI drive?
> You get what you pay for.
Not necessarly. I took this from the 2nd part of 2 in the FAQ of
comps.periphs.scsi:
:QUESTION: Why is SCSI more expensive than IDE?
:ANSWER From: landis@sugs.tware.com (Hale Landis)
:====
:The real reason SCSI costs more has to do with production volume.
:There are about 120,000 drives made per day on this planet. 85%
:of those drives are ATA. The remainder are SCSI, IPI, SMD and a
:few other strange interfaces. The actual percent that are SCSI
:is falling at a very very slow rate. Without the production
:volume, componet prices are higher, therefor drive prices are
:higher.
:
:You figure out how to get people to buy more SCSI drives, say
:50,000 per day, and maybe the prices will come down to ATA price
:levels. Plus you could probably get a very good marketing job at
:any of the disk drive companies! Of course, each day more and
:more people are discovering the performance advantage of ATA so
:your job may not be as easy as you would like.
I know that SCSI is "intelligent" but does that really prevails over
mass production? Anyway I don't care because I get the same price
for the 540Mb drive with SCSI or IDE interface and I already have the
ADAPTEC card.
Concerning the performance, and with this I would like to answer to
michaelv@iastate.edu (Michael L. VanLoon) too, who writes:
>There is a big win in getting SCSI devices. SCSI is faster and
>flexible than IDE,
Agreed, I could install the same HD on other machines, eventually a
RISC one.
> and a SCSI controller takes a lot of load off the
>CPU, where IDE makes the CPU do all the work in transferring files.
>
>>As far as I understood (was told) there would not be any sensible difference
>>for a one or two HD stations ("the botleneck is the bus speed" they said).
>
>This is untrue, to a point. Through an ISA bus, you may not get any
>extra speed with SCSI on raw disk transfers. However, since the SCSI
>controller is doing all the work as a bus-master, your CPU will be
>free to do other things while the transfer is taking place. With IDE,
>the CPU is totally dedicated to writing every byte out and reading
>every byte in from the IDE drive in a tight loop, meaning it can do
>nothing else while an IDE transfer is in progress.
>
>So, even if disk transfers aren't any faster for you, your machine,
>overall, will be less busy with SCSI, and may perform more "smoothly".
>
>Now, in your case, you have a very slow SCSI card,
> ^^^^
> so the bus speed is going to limit you more than anything else.
^^^ ^^^^^
You mean ("narrow SCSI"=16 bits connection trough the ISA
bus) in contrast to wide SCSI (32 bits trough local bus). Am I right?
After all thats why the "F" in AHA1542CF, for Fast SCSI.
> You might start out with your current SCSI card, than upgrade to a
> BusLogic SCSI card that works in one of your VLB slots (four to eight
> times faster) at some point in the future, which will work with your
> current SCSI drives.
Well, with 10 Mbps instead of up to 40 with WIDE SCSI, is not that bad,
so let me quote what I find in the answer to the same (previous FAQ)
question:
:In a typical single drive PC system, ATA (you call it IDE, the
:proper name is ATA) is faster than any SCSI. This is because of
^^^^^^
:the 1 to 2 millisecond command overhead of a SCSI host adapter
:vs. the 100 to 300 microsecond command overhead of an ATA drive.
:Also, ATA transfers data 16-bits at a time from the drive
:directly to/from the system bus. Compare this to SCSI which
:transfers data 8-bits at a time between the host adapter and the
:drive. The host adapter may be able to transfer data 16-bits at
:a time to the system bus.
:
:Of course you could go to Fast SCSI or Wide SCSI but that costs
:a whole bunch more!
:
Oooop! But I have Fast SCSI!!! I am really confused now... (Can
anybody explain if FAST SCSI resolves the command overhead problem?
and the SCSI to drive 8-bits data transfer? is this because of the Z80
processor in the AHA1542CF card?
:But then you asked about cost.
:
:And then you must add in the host adapter cost. Compare $15 for
:ATA vs. $50 for a simple SCSI host adapter. But you probably
:want a higher quality SCSI host adapter so plan on spending $100
:to $500 for one.
:
I am ignorant about hardware considerations. The only thing I would like
to know is wether performance of the system I have now will be better
with the IDE or the SCSI drive.
Flexibility of SCSI is the other valid point but I am not giving
too much weight to it right now. Maybe tomorrow, :-)
Thank you all of you. keep listening pros and cons.
Lazaro (a patient buyer)
P.S. Lapsus:
>-> SCASI Adapter Card (ADAPTEC 1542CF),
> It's *SCSI*! Repeat after me: S - C - S - I
> It stands for Small Computer Systems Interface
Sorry, I already wrote "SCSI" 100 time on a A4 sheet)
>>a Quantum 420Mb.
>I have one of these -- it's an excellent drive.
Really? I was told that Quantum was going to modify the 340Mbs
so as to obtain a 420Mb HD (they did something similar
with the 240->270 some months ago) and call the dealer to confirm,
and he said: "whaaaaaattttt ?????????"