Date: Thu, 6 Apr 2006 09:16:33 +0300 From: Vasil Dimov <vd@FreeBSD.org> To: Thiago Damas <tdamas@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: odd behavior with geom - gmirror - read/write simultaneously Message-ID: <20060406061633.GA79708@qlovarnika.bg.datamax> In-Reply-To: <f8e3d83f0604051109s774f7e1cr90601e78e9a77d15@mail.gmail.com> References: <f8e3d83f0604051109s774f7e1cr90601e78e9a77d15@mail.gmail.com>
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On Wed, Apr 05, 2006 at 03:09:56PM -0300, Thiago Damas wrote:
> Hi,
> I'm having a odd behavior while using geom_mirror.
> I have the following situation:
> - RAID1 with 2 SATA disks
> # gmirror status
> Name Status Components
> mirror/home0 COMPLETE ad2
> ad3
>=20
> - home0 as /home
> # df -h
> Filesystem Size Used Avail Capacity Mounted on
> /dev/ad0s1a 1.9G 74M 1.7G 4% /
> devfs 1.0K 1.0K 0B 100% /dev
> /dev/ad0s1d 989M 16K 910M 0% /tmp
> /dev/ad0s1e 7.7G 1.9G 5.2G 27% /usr
> /dev/ad0s1f 58G 139M 53G 0% /var
> /dev/mirror/home0s1c 226G 7.4G 200G 4% /home
>=20
> I was testing the read/write speed on /home, with:
> # dd if=3D/dev/ad0 of=3D/home/test.data bs=3D4m
> While running this, gstat shows me what I wanted:
> # gstat
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 0 230 230 29383 1.9 0 0 0.0 42.8| ad0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1
> 9 192 0 0 0.0 192 24529 21.0 65.3| ad2
> 7 196 0 0 0.0 196 25040 16.6 65.4| ad3
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1a
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1b
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1c
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1d
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1e
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1f
> 0 0 0 0 0.0 0 0 0.0 0.0| ad2s1
> 9 192 0 0 0.0 192 24529 21.2 65.4| mirror/hom=
e0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad3s1
> 9 192 0 0 0.0 192 24529 21.2 65.4| mirror/hom=
e0s1
> 9 192 0 0 0.0 192 24529 22.0 66.6| mirror/hom=
e0s1c
>=20
> After that, I test the read speed:
> # dd if=3D/home/test.data bs=3D4m of=3D/dev/null
> # gstat
> dT: 0.501 flag_I 500000us sizeof 240 i -1
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1
> 1 120 120 15329 3.7 0 0 0.0 44.9| ad2
> 0 122 122 15584 3.5 0 0 0.0 43.1| ad3
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1a
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1b
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1c
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1d
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1e
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1f
> 0 0 0 0 0.0 0 0 0.0 0.0| ad2s1
> 1 242 242 30913 3.7 0 0 0.0 88.4| mirror/hom=
e0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad3s1
> 1 242 242 30913 3.7 0 0 0.0 88.7| mirror/hom=
e0s1
> 1 242 242 30913 3.7 0 0 0.0 90.0| mirror/hom=
e0s1c
>=20
> And it shows again what was supposed to.
>=20
> Now, I test read/write simultaneously:
> In on shell (1):
> # dd if=3D/dev/ad0 of=3D/home/test.data bs=3D4m
> After some time, in another shell(2)
> # dd if=3D/home/test.data bs=3D4m of=3D/dev/null
> And gstat shows me the following:
> # gstat
> dT: 0.501 flag_I 500000us sizeof 240 i -1
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1
> 0 158 158 20183 3.0 0 0 0.0 47.6| ad2
> 1 158 158 20183 2.5 0 0 0.0 39.1| ad3
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1a
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1b
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1c
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1d
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1e
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1f
> 0 0 0 0 0.0 0 0 0.0 0.0| ad2s1
> 1 315 315 40367 2.8 0 0 0.0 87.4| mirror/hom=
e0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad3s1
> 1 315 315 40367 2.8 0 0 0.0 87.8| mirror/hom=
e0s1
> 1 315 315 40367 2.8 0 0 0.0 89.4| mirror/hom=
e0s1c
>=20
>=20
> I'm having NO writes in home0; even hitting ^C in shell(1) hangs,
> until I cancel the dd command in shell(2).
> I think its happening some problem with geom code . Can someone
> verify this? I using 6.1 PRERELEASE, with GENERIC kernel.
>=20
Did you try the parallel dd commands on another partition which is not
gmirror'd? For example:
dd if=3D/dev/ad0 of=3D/var/tmp/test.data bs=3D4m
dd if=3D/var/tmp/test.data bs=3D4m of=3D/dev/null
So you can be sure that it is a gmirror issue.
When I try your test on my mirror gstat shows read and write activity,
but the reading dd quits very soon, because reading appears to be faster
than writing.
I would suggest that you write to one file and read from another file
when you do the parallel test.
Just a hint: for the write test you should better use /dev/zero instead
of /dev/ad0 - ``dd if=3D/dev/zero of=3D/home/test.data bs=3D4m'' for obvious
reasons.
--=20
Vasil Dimov
gro.DSBeerF@dv
Testing can show the presence of bugs, but not their absence.
-- Edsger W. Dijkstra
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