Hi all!
I have a system (obsd3.8/sparc64) with 2 identical scsi drives (4
partitions + 1 swap each). The largest partition (10G) is mirrored over
the 2 drives as a ccd with interleave factor 16.
When running iostat during an I/O stress test (writing many small files
to the ccd in 10 parallel threads), the output shows different values
for KB/t and t/s respectively for the physical drives and the ccd.
Sample lines look like
tty sd0 sd1 ccd0 cpu
tin tout KB/t t/s MB/s KB/t t/s MB/s KB/t t/s MB/s us ni sy in id
0 4 6.34 199 1.23 6.20 200 1.21 9.94 125 1.22 2 0 3 2 93
0 90 6.07 217 1.28 5.90 188 1.09 8.88 125 1.09 2 0 4 1 93
0 30 6.03 210 1.23 5.83 237 1.35 8.64 160 1.35 0 0 1 2 96
To my understanding this shows that larger blocks are written to the ccd
in less transfers than to the physical disks, tantamounting to the same
absolute data amount (iostat -I shows similar figures). When trying to
understand the relationship between the single transfer rates (~6 KB/t
in ~200 t/s on the physical disks and ~10 KB/t in ~120 t/s on the ccd) I
realized that my knowledge doesn't suffice.
Does anybody know how those figures relate? Where are those block sizes
specified?
And 1.2M/s is rather less that what I'd have expected, is this figure
really the disk transfer rate?
Thanks for any hint.
/markus
