On 03/02/07 06:03, Alexander Leidinger wrote:
Quoting Cheffo <[EMAIL PROTECTED]> (from Fri, 02 Mar 2007 13:38:45 +0200):
Hi,
Ted Mittelstaedt wrote:
----- Original Message ----- From: "O. Hartmann"
<[EMAIL PROTECTED]>
To: <freebsd-performance@freebsd.org>; <freebsd-questions@freebsd.org>
Sent: Friday, March 02, 2007 1:38 AM
Subject: (S)ATA performance in FBSD 6.2/7.0
The last days I tried to figure out why some of my lab's FreeBSD
boxes and also mine at home seem to be outperformed by some Linux
setups around here and I saw something interesting.
blah blah blah deleted
Before digging into this problem deeper with benchmarks, could
anyone explain why FreeBSD reaches this 33 MB/s limit (sounds like
UDMA 33
man mount
read section on "async"
linux by default mounts async
freebsd by default mounts sync
you can change FBSD to async
then watch your fs scramble during a power failure
no big deal, it's only your data.
Ted
If SYNC is default how can you explain this:
[12:[EMAIL PROTECTED]:~# mount
/dev/ad4s3a on / (ufs, local, synchronous)
devfs on /dev (devfs, local)
/dev/ad4s3d on /tmp (ufs, local, soft-updates)
/dev/ad4s3f on /usr (ufs, local, soft-updates)
/dev/ad4s3e on /var (ufs, local, soft-updates)
[...]
So I'm pretty sure that for type ufs async is default.
Both of you are wrong. By default "noasync" is used. This is different
from sync and async. Feel free to look up the difference.
Also I do not see why sync should report different speeds for copy and
benchmark tools if they do the same thing?
Because cp may behave differently than the tools used to benchmark. A
dd may be more portable in this case.
Just to be sure I added to my /tmp entry async in /etc/fstab:
/dev/ad4s3d /tmp ufs rw,async 2 2
umounted and mounted again and still have:
/dev/ad4s3d on /tmp (ufs, local, soft-updates)
IIRC when SU is used, async is not used even if specified. But I' not
sure about this.
Asides from the linux async-by-default there's maybe also the
write-cache-off penalty in FreeBSD. But I'm not sure it is off by
default. I disable the WC myself in loader.conf everywhere to be on
the safe side and I don't feel like experimenting ATM (I'm ill in bed).
If the same conditions are tested in FreeBSD and linux (which is not
easy, as we don't share a common FS implementation, even when we
support the same FS type) and the sync/async and WC related stuff can
be ruled out, it may be a problem in the (S)ATA code and it would be
nice if we would know about this. So please dig deeper into this (it
can also be a problem with our cp or GEOM or whatever).
People should not be using file system tools to measure hardware speeds
like SATA or disks. That doesn't make sense, since a portion of that
benchmark would then include the file system, which as you mention is
very very different between OS'es. cp shouldn't be used. dd is ok for
bare minimum testing I suppose.
On one of my SATA memory disks, I can get 125MB/s through it, with no
extra magic.
Eric
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