Date: Thu, 6 Apr 2006 11:24:34 -0300 From: "Thiago Damas" <tdamas@gmail.com> To: vd@freebsd.org Cc: freebsd-hackers@freebsd.org Subject: Re: odd behavior with geom - gmirror - read/write simultaneously Message-ID: <f8e3d83f0604060724h716afe61s372838a9b5589a3e@mail.gmail.com> In-Reply-To: <20060406061633.GA79708@qlovarnika.bg.datamax> References: <f8e3d83f0604051109s774f7e1cr90601e78e9a77d15@mail.gmail.com> <20060406061633.GA79708@qlovarnika.bg.datamax>
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Hi,
same problem:
* in shell(1):
# dd if=3D/dev/zero of=3D/var/tmp/test bs=3D4m
* after some time (=3D~ 20seconds), in shell(2)
# dd if=3D/var/tmp/test bs=3D4m of=3D/dev/null
gstat shows no writes again, only reads; hitting ^C in shell(1), it
hangs until the dd in shell(2) finishes.
Using diferents files (after rebooting the machine to prevent some cache)=
:
In:
same problem:
* in shell(1):
# dd if=3D/dev/zero of=3D/var/tmp/test bs=3D4m
* after some time (=3D~ 20seconds), in shell(2)
# dd if=3D/var/tmp/test bs=3D4m of=3D/dev/null
gstat shows no writes again, only reads; hitting ^C in shell(1), it
hangs until the dd in shell(2) finishes.
Using diferents files (after rebooting the machine to prevent some
cache), I found the inverse situation:
* in shell(1):
# dd if=3D/dev/zero of=3D/var/tmp/test2 bs=3D4m
* in shell(2):
# dd if=3D/var/tmp/test of=3D/dev/null bs=3D4m
gstat shows 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
11 357 0 0 0.0 357 45737 14.2 99.7| ad0
11 357 0 0 0.0 357 45737 14.3 99.7| ad0s1
0 0 0 0 0.0 0 0 0.0 0.0| ad2
0 0 0 0 0.0 0 0 0.0 0.0| 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
11 357 0 0 0.0 357 45737 15.1 99.7| ad0s1f
0 0 0 0 0.0 0 0 0.0 0.0| ad2s1
0 0 0 0 0.0 0 0 0.0 0.0| mirror/home0
0 0 0 0 0.0 0 0 0.0 0.0| ad3s1
0 0 0 0 0.0 0 0 0.0 0.0| mirror/home0=
s1
0 0 0 0 0.0 0 0 0.0 0.0| mirror/home0=
s1c
Hitting ^C in shell(2), it hangs until I cancel the dd of shell(1),
and shows the following:
# dd if=3D/var/tmp/test of=3D/dev/null bs=3D4m
^C0+0 records in
0+0 records out
0 bytes transferred in 23.318283 secs (0 bytes/sec)
In:
> 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.
try waiting a little more before execute the dd command.
After those tests, the problem isnt relationated with GEOM, I think.
What can I do now?
>
> 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 obvi=
ous
> reasons.
>
> --
> Vasil Dimov
> gro.DSBeerF@dv
>
> Testing can show the presence of bugs, but not their absence.
> -- Edsger W. Dijkstra
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