Date: Wed, 20 Aug 1997 00:32:51 -0700 (PDT) From: Simon Shapiro <Shimon@i-Connect.Net> To: Tom Samplonius <tom@sdf.com> Cc: scsi@FreeBSD.ORG, Curt Welch <curt@kcwc.com> Subject: Re: expected performance with DPT RAID-5... Message-ID: <XFMail.970820003251.Shimon@i-Connect.Net> In-Reply-To: <Pine.BSF.3.95q.970817195747.28679B-100000@misery.sdf.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Hi Tom Samplonius; On 18-Aug-97 you wrote:
...
> "cd" to one of the RAID-5 file systems and do a "dd if=/dev/zero
> of=testfile bs=64k count=1000". That will create a file called
> "testfile"
> 64MB in length (64k x 1000), and tell you how long it took to write it.
>
> Then reboot (the only way I know of clearing the FreeBSD file cache,
> and
> the DPT cache), and do a "dd if=testfile bs=64k of=/dev/null" to read the
> file back.
If you unmount the filesystems and make sure no other process has any of
the device open, the caches will be flushed. The O/S must do so in case
of removable media. The DPT firmware flushes caches in response to
ALLOW MEDIA REMOVAL which is issued by sd.c in response to a close call.
> On the write test I get about 3500000 bps, and the write test about
> 9200000 bps. These results don't seem very good too me.
For a RAID-5? Your WRITE is a bit (40%?) slow. READ is about right.
Remember, these are sequential tests. You may want to adjust the
read-ahead cache if this is your typical load (some people enjoy
transferring many zeros from and to the disk :-).
If you want a random test, pick up form my system st.c. It will do random
seeks and either read, write, or read-modify-write and tell you how badly
the system behaves.
An interesting variation is to run, say 256 dd's and 1024 st's.
Then measure throughput for a given stream.
While (or soon after) the test is run do:
(cd /dev;./MAKEDEV dpt0)
echo -n "dump softc" > /dev/dpt0
get_dpt /dev/dpt0
Then look at the output. Yes, I will write a manpage and a front-end
to this pair. Right now read the source in sys/dev/dpt/dpt_control.c
Will answer many of your questions.
Simon
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?XFMail.970820003251.Shimon>