Date: Sat, 6 Nov 1999 03:32:11 -0800 From: John-Mark Gurney <gurney_j@efn.org> To: Rob Snow <rsnow@lgc.com> Cc: freebsd-questions@freebsd.org Subject: Re: writing much slower than reading... Message-ID: <19991106033211.51337@hydrogen.fircrest.net> In-Reply-To: <38240CC0.8099D19D@lgc.com>; from Rob Snow on Sat, Nov 06, 1999 at 05:10:56AM -0600 References: <19991106013045.13836@hydrogen.fircrest.net> <38240CC0.8099D19D@lgc.com>
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Rob Snow scribbled this message on Nov 6:
> Emm, I want your system. Have you double checked your numbers? They
> look a bit high. Here's what I get on a vinum stripe across two 'cudas
> on an SMP box:
go to IBM's web site and read about the drive... I bought the drive
for $241 at gogocity.com... it's a 27gig 7200rpm drive, and IBM
advertises that the platter speed is 13.8meg/sec to 22meg/sec... the
performance is the main reason that I bought the drive... :)
also, don't forget I'm using the raw device, so there isn't any buffer
like if I was going through the file system...
just so you know, I went and grabed rawio to run on the disk:
$ rawio -c 128 -r -w /dev/rwd0s1g
Random read Sequential read Random write Sequential write
ID K/sec /sec K/sec /sec K/sec /sec K/sec /sec
anon 29293.9 447 28755.4 439
the -c 128 sets it for 64k transfers, and by default does 16384
transfers, so we were transfering 1gig of data... the raw partition
is actually a couple gigs into the drive... and is ~25gigs large...
> rsnow@basil% time dd if=/dev/vinum/rstripe of=/dev/null bs=64k
> count=2048
> 2048+0 records in
> 2048+0 records out
> 134217728 bytes transferred in 7.938773 secs (16906609 bytes/sec)
> 0.007u 0.520s 0:07.98 6.5% 73+371k 2+0io 0pf+0w
> John-Mark Gurney wrote:
> >
> > well, I am working on writing a capture program to do 640x480x12bpp@30fps
> > to a raw disk, but writing to the raw device is SOOO slow... the reason
> > I say it's slow is the fact that it takes 8 times the system time writing
> > than reading...
> >
> > a bit about the system... k6/2-250, 100mhz system bus, pc100 64meg dimm,
> > VIA MVP3 chipset (IDE DMA enabled), IBM-DPTA-372730 hard disk, Hauppauge
> > WinCast/TV Model 61351 B226, 3.3-RELEASE...
> >
> > now the hard disk can push and pull around 20meg/sec w/o any problems..
> > but when I time the disk I get:
> > $ time dd if=/dev/rwd0s1g of=/dev/null bs=64k count=2048
> > 2048+0 records in
> > 2048+0 records out
> > 134217728 bytes transferred in 5.747521 secs (23352281 bytes/sec)
> > 5.75 real 0.01 user 0.21 sys
> > $ time dd if=/dev/zero of=/dev/rwd0s1g bs=64k count=2048
> > 2048+0 records in
> > 2048+0 records out
> > 134217728 bytes transferred in 6.281820 secs (21366057 bytes/sec)
> > 6.28 real 0.00 user 1.68 sys
> >
> > now, why does it cost SOOO much more processing time to write than
> > read?? are there plans to fix this slow down? is it possible? can't
> > we just dma write out of userland since we are blocking on the write?
--
John-Mark Gurney Voice: +1 408 975 9651
Cu Networking
"The soul contains in itself the event that shall presently befall it.
The event is only the actualizing of its thought." -- Ralph Waldo Emerson
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