Subject: Re: Disk performance under NetBSD on A3000
To: Eduardo E. Horvath firstname.lastname@example.org <email@example.com>
From: Andreas Johansson <firstname.lastname@example.org>
Date: 04/25/1995 01:39:49
According to Eduardo E. Horvath email@example.com:
> On Sun, 23 Apr 1995, Stephen J. Roznowski wrote:
> > I'm seeing poor disk performance under NetBSD-current on my A3000.
> > Under ADOS, I see about 1.7-2.0 megabytes per second (via sysinfo)
> > while under NetBSD, I see about 500 kilobytes per second
> > (dd if=/dev/zero of=zzzzz bs=1024k count=10).
> 1) You are measuring write performance, not read performance. Writes are
> usually 1/2 to 1/4 the speed of reads.
Not my experience with my system. Write: 550kB/s, read 650kB/s.
System described in my last letter.
> 2) You are writing to a file within the filesystem, which involves such
> things as file-system overhead, copying from your process space into the
> buffer cache, and updating the filesystem structures.
Yep, but couldn't this somehow be done more efficiently, the A3640 in my
system isn't that quick in moving data...
Under ados I have tried a memorymoverprogram.
Writes: 6.?Mb/s (due to copyback cache).
Moving data like this isn't exactly improving disk performance.
Some speed could be won by using the move16 instruction (with it's alignment
problems (?)) or disabling the datacache while moving with a 040. Is
anything done to improve speed on a 3640?
> 3) You are writing 1K at a time, where the filesystem is using 8K
> blocks. This means you will probably be doing 4 writes/block.
You are misreading the dd command, it says bs=1024k <---.
> > What disk performance numbers are others seeing?
> With (dd if=/dev/rs?c of=/dev/null bs=65565) I get on the order of
> 1.5-2.5MB/s, depending on which drive I access.
Well, what about file access (which is the thing we are using in the real
world)? I have 3Mb/s raw speed (the disk and SCSI interface actually can
produce 4.5Mb/s), but that doesn't help the filesystem speeds of 650kB/s.
This figure probably wouldn't change much with a slower disk - so why
should I have a fast disk with NetBSD?
BTW: I haven't tried the tunefs thing, I haven't been able to see the
current value either.
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