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Subject: Re: IBM blade server abysmal disk write performances
From: Dieter BSD <dieterbsd@gmail.com>
To: freebsd-hackers@freebsd.org
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> 25.9 MB/s

Even Linux is pretty slow.

> Transfer rates:
>         outside:       102400 kbytes in   0.685483 sec = 149384 kbytes/sec
>         middle:        102400 kbytes in   0.747424 sec = 137004 kbytes/sec
>         inside:        102400 kbytes in   1.051036 sec = 97428 kbytes/sec

That's more like it.  I assume these numbers are reading.  You should get
numbers nearly this high when writing.

Can you try writing to the bare drive without a filesystem?

time dd if=/dev/da0 of=/dev/null bs=124k count=250000
time (dd if=/dev/zero if=/dev/da0 bs=124k count=250000; sync)

Between writing more data than the size of memory and the sync,
this should hopefully reduce any buffering effects down into the noise
and make the numbers more comparable between FreeBSD and Linux.
(and more honest) Also eliminates any effect from the filesystem, which
will be different between FreeBSD and Linux.

Writing should be almost as fast as reading.

Is the disk healthy?  Smartctl might give a clue.

If the disk is healthy and you still get numbers that indicate one
write per rev without a filesystem, then the question is why does
the driver claim queueing but not deliver it?