Reading from ZFS mirror 2x slower than expected?

[Urmas Lett]

While reading from simple zfs mirror 'dd if=zfs.test of=/dev/null 
bs=512k' systat -vm shows individual disks only 50% busy:

Disks   ad4   ad8  ad10
KB/t   0.00   128   128
tps       0   273   285
MB/s   0.00 34.15 35.64
%busy     0    51    48

reading from one disk 'dd if=/dev/ad8 of=/dev/null bs=512k' is 2x faster:

Disks   ad4   ad8  ad10
KB/t   0.00   128  0.00
tps       0   769     0
MB/s   0.00 96.09  0.00
%busy     0    97     0

and even writing to the same mirror is 2x faster:

Disks   ad4   ad8  ad10
KB/t   0.00   128   128
tps       0   654   707
MB/s   0.00 81.76 88.36
%busy     0   100   100



-- 
Urmas Lett

Tel:    +(372) 7 302 110
Fax:    +(372) 7 302 111
E-Mail: urmas.lett at eenet.ee