From owner-freebsd-hackers  Tue Sep 19  8:42:32 2000
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Date: Tue, 19 Sep 2000 11:45:40 -0400 (EDT)
From: Marc Tardif <intmktg@CAM.ORG>
To: freebsd-fs@freebsd.org, freebsd-hackers@freebsd.org
Subject: device timings
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Considering the following disk configuration:
******* Working on device /dev/rwd0 *******
parameters extracted from in-core disklabel are:
cylinders=256 heads=132 sectors/track=63 (8316 blks/cyl)

parameters to be used for BIOS calculations are:
cylinders=256 heads=132 sectors/track=63 (8316 blks/cyl)

Media sector size is 512
Warning: BIOS sector numbering starts with sector 1
Information from DOS bootblock is:
The data for partition 1 is:
sysid 165,(FreeBSD/NetBSD/386BSD)
    start 63, size 1937565 (946 Meg), flag 80 (active)
        beg: cyl 0/ sector 1/ head 1;
        end: cyl 232/ sector 63/ head 131
The data for partition 2 is:
sysid 0,(unused)
    start 1937628, size 58212 (28 Meg), flag 0
        beg: cyl 233/ sector 1/ head 0;
        end: cyl 239/ sector 63/ head 131
...

Now considering the following timings done with dd, how come I get such
different transfer rates (bytes/sec) for s1 and s2? I understand there
should be a difference between the block and character interface, as shown
in the first two timings, but why isn't the same difference shown for the
last two timings?

# dd if=/dev/wd0s1 of=/dev/null bs=8316b count=5
5+0 records in
5+0 records out
21288960 bytes transferred in 8.580486 secs (2481090 bytes/sec)

# dd if=/dev/rwd0s1 of=/dev/null bs=8316b count=5
5+0 records in
5+0 records out
21288960 bytes transferred in 4.058639 secs (5245344 bytes/sec)

# dd if=/dev/wd0s2 of=/dev/null bs=8316b count=5
5+0 records in
5+0 records out
21288960 bytes transferred in 6.066568 secs (3509226 bytes/sec)

# dd if=/dev/rwd0s2 of=/dev/null bs=8316b count=5
5+0 records in
5+0 records out
21288960 bytes transferred in 6.015735 secs (3538879 bytes/sec)



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