Date: Wed, 11 Nov 1998 16:20:00 +1030 From: Greg Lehey <grog@lemis.com> To: john cooper <john@isi.co.jp>, hackers@FreeBSD.ORG, mike@smith.net.au, ticso@cicely.de Subject: Re: SCSI vs. DMA33.. Message-ID: <19981111162000.O20374@freebie.lemis.com> In-Reply-To: <98Nov11.134648jst.21907@ns.isi.co.jp>; from john cooper on Wed, Nov 11, 1998 at 01:41:00PM %2B0900 References: <98Nov11.134648jst.21907@ns.isi.co.jp>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wednesday, 11 November 1998 at 13:41:00 +0900, john cooper wrote:
>
> Hi,
> Just wondering if anyone has any _objective_ opinion on
> the performance of say wide SCSI2 vs. DMA33 IDE drives [running
> on contemporary motherboards].
Depends on what you mean by "objective".
> The theoretical throughputs of 40MBs and 33MBs don't tell me a whole
> lot. I know SCSI was the choice for performance in the past,
> however I'm curious what others are seeing in actual usage these
> days.
SCSI is still the performance choice, but the field is closer now. I
have five drives on my main machine:
wd0: 1223MB (2504880 sectors), 2485 cyls, 16 heads, 63 S/T, 512 B/S
wd2: 6197MB (12692736 sectors), 12592 cyls, 16 heads, 63 S/T, 512 B/S
ide_pci: generic_dmainit 0170:1: warning, IDE controller timing not set
wdc1: unit 1 (wd3): <IBM-DHEA-38451>, DMA, 32-bit, multi-block-16
wd3: 8063MB (16514064 sectors), 16383 cyls, 16 heads, 63 S/T, 512 B/S
ahc0: <Adaptec 2940 SCSI adapter> rev 0x03 int a irq 11 on pci0.9.0
ahc0: aic7870 Single Channel A, SCSI Id=7, 16/255 SCBs
da0 at ahc0 bus 0 target 0 lun 0
da0: <IBM DORS-32160 WA0A> Fixed Direct Access SCSI2 device
da0: 10.0MB/s transfers (10.0MHz, offset 15), Tagged Queueing Enabled
da0: 2063MB (4226725 512 byte sectors: 64H 32S/T 2063C)
da1 at ahc0 bus 0 target 2 lun 0
da1: <CONNER CFP4207S 4.28GB 2847> Fixed Direct Access SCSI2 device
da1: 3.300MB/s transfers, Tagged Queueing Enabled
da1: 4096MB (8388608 512 byte sectors: 64H 32S/T 4096C)
I'm running 3.0-CURRENT (post-RELEASE), and as you can see Ultra DMA
is enabled on the IDE drives. Here's what I get transferring 32 MB
from each raw device:
$ dd if=/dev/rwd0c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 6.938876 secs (4722379 bytes/sec)
$ dd if=/dev/rwd2c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 3.214075 secs (10195157 bytes/sec)
$ dd if=/dev/rwd3c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 3.278695 secs (9994220 bytes/sec)
$ dd if=/dev/rda0c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 5.734632 secs (5714055 bytes/sec)
$ dd if=/dev/rsd1c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 8.893227 secs (3684602 bytes/sec)
Looks good for the IDE drives, doesn't it? They say, though, that
SCSI drives work better with multiple requests outstanding...
$ dd if=/dev/rsd0c bs=32k count=1000 of=/dev/null & dd if=/dev/rsd1c bs=32k count=1000 of=/dev/null
[3] 20705
32768000 bytes transferred in 9.940641 secs (3296367 bytes/sec)
32768000 bytes transferred in 12.121225 secs (2703357 bytes/sec)
$ dd if=/dev/rsd0c bs=32k count=1000 of=/dev/null & dd if=/dev/rsd1c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 9.940080 secs (3296553 bytes/sec)
32768000 bytes transferred in 12.080951 secs (2712369 bytes/sec)
Well, that doesn't look spectacular. What about the IDE drives (both
on the same controller, wdc1):
$ dd if=/dev/rwd2c bs=32k count=1000 of=/dev/null & dd if=/dev/rwd3c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 3.710713 secs (8830648 bytes/sec)
32768000 bytes transferred in 3.711320 secs (8829204 bytes/sec)
$ dd if=/dev/rwd2c bs=32k count=1000 of=/dev/null & dd if=/dev/rwd3c bs=32k count=1000 of=/dev/null
32768000 bytes transferred in 3.737548 secs (8767245 bytes/sec)
32768000 bytes transferred in 3.729290 secs (8786659 bytes/sec)
I must say, I'm surprised. This makes it look like there's more of a
performance hit with concurrent requests on SCSI than on IDE. Let's
look at the performance hits as a percentage (there's some guesswork
which is which, of course, but only a little):
alone 2 together % drop
wd2 10.2 8.8 14
wd3 10.0 8.8 12
da0 5.7 3.3 42
da1 3.7 2.7 23
OK, the controller I have isn't the newest, but there's not exactly a
lot of data crossing: even with the two disks transferring by
themselves, they're transferring less data than a single DHEA drive.
Can anybody else think of a reason for this? I have a 2940 Ultra
("ahc0: <Adaptec 2940 Ultra SCSI adapter> rev 0x00 int a irq 14 on
pci0.17.0") in another machine. The disks aren't Ultra SCSI; is there
any reason to think it will perform better?
Greg
--
See complete headers for address, home page and phone numbers
finger grog@lemis.com for PGP public key
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?19981111162000.O20374>