gvinum mirror seems to use only one disk for reading

[Deomid Ryabkov]

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 at rojer.pp.ru
rojer at sysadmins.ru
ICQ: 8025844

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