Date: Tue, 28 Aug 2007 10:02:50 -0700 (PDT) From: Simun Mikecin <numisemis@yahoo.com> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: freebsd-fs@freebsd.org Subject: Re: zfs and BIO_FLUSH on amr(4) Message-ID: <397419.50435.qm@web36604.mail.mud.yahoo.com> In-Reply-To: <20070828105435.GC36596@garage.freebsd.pl>
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--- Pawel Jakub Dawidek <pjd@FreeBSD.org> wrote:
> On Tue, Aug 28, 2007 at 03:00:44AM -0700, Simun Mikecin wrote:
> > amr(4) can have onboard cache memory with or without battery backup. Is BIO_FLUSH call really
> > needed when amr(4) is used with onboard cache memory with a battery backup?
> I don't think so. The thing is that when ZFS receives information that
> write is done, it should be on disk (at some point) and you
> battery-backed cache should ensure that. You can turn off sending
> BIO_FLUSH by setting vfs.zfs.cache_flush_disable to 1 (in
> /boot/loader.conf).
>
> BTW. How big performance drop do you see with BIO_FLUSH turned on?
Not much according to bonnie++:
Results from running "bonnie++ -d /var/tmp/test -s 4g -n 100 -u someuser:somegroup"
With vfs.zfs.cache_flush_disable=0:
Version 1.93c ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
data.home.hr 4G 105 97 57927 15 44814 11 261 97 150219 17 281.0 4
Latency 147ms 1669ms 964ms 83179us 551ms 241ms
Version 1.93c ------Sequential Create------ --------Random Create--------
data.home.hr -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
100 19034 92 28638 98 10672 91 13761 98 32042 97 14009 95
Latency 77131us 2460us 3298us 153ms 7728us3796us
With vfs.zfs.cache_flush_disable=1:
Version 1.93c ------Sequential Output------ --Sequential Input- --Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
data.home.hr 4G 118 94 67671 16 41687 10 292 99 154120 20 290.1 4
Latency 764ms 1743ms 1586ms 78276us 342ms 245ms
Version 1.93c ------Sequential Create------ --------Random Create--------
data.home.hr -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
100 22064 91 33277 97 13824 93 16720 86 23878 99 10182 95
Latency 68420us 2832us 3789us 727ms 7670us 3838us
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