Date: Fri, 02 Mar 2007 13:03:46 +0100 From: Alexander Leidinger <Alexander@Leidinger.net> To: Cheffo <cheffo@FreeBSD-BG.org> Cc: freebsd-performance@freebsd.org, "O. Hartmann" <ohartman@zedat.fu-berlin.de>, freebsd-questions@freebsd.org, Ted Mittelstaedt <tedm@toybox.placo.com> Subject: Re: (S)ATA performance in FBSD 6.2/7.0 Message-ID: <20070302130346.1ipa5epugws4scgw@webmail.leidinger.net> In-Reply-To: <45E80CC5.8080607@FreeBSD-BG.org> References: <45E7F09B.7070005@zedat.fu-berlin.de> <00c401c75caf$89ee3370$3c01a8c0@coolf89ea26645> <45E80CC5.8080607@FreeBSD-BG.org>
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Quoting Cheffo <cheffo@FreeBSD-BG.org> (from Fri, 02 Mar 2007 13:38:45 +0200= ): > Hi, > > > Ted Mittelstaedt wrote: >> ----- Original Message ----- From: "O. Hartmann" =20 >> <ohartman@zedat.fu-berlin.de> >> 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 =20 >>> boxes and also mine at home seem to be outperformed by some Linux =20 >>> setups around here and I saw something interesting. >>> >> >> blah blah blah deleted >> >>> Before digging into this problem deeper with benchmarks, could =20 >>> anyone explain why FreeBSD reaches this 33 MB/s limit (sounds like =20 >>> 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: > > [12:58]root@hater:~# 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 =20 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 =20 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 =20 sure about this. Asides from the linux async-by-default there's maybe also the =20 write-cache-off penalty in FreeBSD. But I'm not sure it is off by =20 default. I disable the WC myself in loader.conf everywhere to be on =20 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 =20 easy, as we don't share a common FS implementation, even when we =20 support the same FS type) and the sync/async and WC related stuff can =20 be ruled out, it may be a problem in the (S)ATA code and it would be =20 nice if we would know about this. So please dig deeper into this (it =20 can also be a problem with our cp or GEOM or whatever). Bye, Alexander. --=20 "I heard one time you single-handedly defeated a hoard of rampaging of somethings in the something something system." -Fry http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID =3D B0063FE7 http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID =3D 72077137
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