Date: Wed, 02 Mar 2005 17:37:06 +0300 From: Deomid Ryabkov <myself@rojer.pp.ru> To: freebsd-geom@freebsd.org Subject: gvinum mirror seems to use only one disk for reading Message-ID: <4225CF92.80800@rojer.pp.ru>
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I have a gvinum-based mirrored setup and i noticed that only one disk
gets the load of read requests.
for example:
toxin[~rojer]# dd if=/dev/gvinum/usr of=/dev/null & vmstat 1
[1] 70487
procs memory page disks faults cpu
r b w avm fre flt re pi po fr sr da0 da1 in sy cs us
sy id
1 1 0 75580 158780 337 0 0 0 395 4 0 0 384 681 1015
4 3 93
1 0 0 75580 158780 3 0 0 0 3 0 0 1964 6376 4138 58340
0 49 51
0 1 0 75580 158780 0 0 0 0 0 0 0 1998 6455 4197 59243
0 52 48
0 1 0 75580 158780 0 0 0 0 0 0 2 1948 6307 4111 57759
1 50 50
0 1 0 75580 158780 0 0 0 0 0 0 0 2007 6492 4217 59502
2 48 50
0 1 0 75580 158780 0 0 0 0 0 0 1 1979 6400 4154 58707
0 48 51
the relevant disk tps values are:
disks
da0 da1
0 0
0 1964
0 1998
2 1948
0 2007
1 1979
notice that only da1 is busy reading, da0 is completely idle.
there is also an oddity when writing to gvinum.
writes go to both drives as they should and tps numbers are the same, as
expected,
but "time spent processing requests" is different for da0 and da1. (this
number is displayed
as "disk percent load" in systat -vmstat).
e.g., when running
dd if=/dev/zero of=/usr/test & systat -vmstat 2
i get output similar to the following:
Disks da0 da1
KB/t 128 128
tps 83 83
MB/s 10.40 10.40
% busy 30 16
the difference stays at about the same value (30 vs 15-17).
the question is... why is that? :)
--
Deomid Ryabkov aka Rojer
myself@rojer.pp.ru
rojer@sysadmins.ru
ICQ: 8025844
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