gstripe small transaction size

[Stephen Sanders]

  I'm trying a disk throughput experiment where in two 3ware raid 6's 
are being put into a g_strip raid 0.

The raid 6's are using 8 7200RPM disks.  The disk transfer rate is 
~80MB/s.  Using a load generation tool that is using O_DIRECT for I/O, 
I've generated the following short output from iostat.  Needless to say, 
the write performance is a lot less than I'm expecting.

We've modified the kernel such that our KB/t figure is closer to 512KB/t 
per disk when measured without the g_strip.  With g_strip turned on, the 
KB/t number is more like 60KB/t.

The question is how do I get g_stripe to write larger transactions to 
the disk ?

Thanks.

gstripe label -v -s 131072 roadkill /dev/da0 /dev/da2
newfs /dev/stripe/roadkill
mount  /dev/stripe/roadkill /u8
sysctl kern.geom.stripe.fast=1

iostat -n3 -t da 5

tty             da0              da1
da2             cpu
tin  tout  KB/t tps  MB/s   KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
0   200 39.52  13  0.49  11.97   1  0.01  41.23  12  0.49   0  0 0 0 100
0    47  0.00   0  0.00   0.00   0  0.00   0.00   0  0.00   0  0 0 0 100
1    19  0.00   0  0.00   0.00   0  0.00   0.00   0  0.00   0  0 0 0 100
20    47  0.00   0  0.00  41.43   3  0.11   0.00   0  0.00   0  0 0 0 100
0    18 56.60 1817 100.41  20.00   1  0.02  57.22 1797 100.44   0 0  6  1 93
0    16 58.87 1978 113.73   0.00   0  0.00  58.27 2000 113.81   0 0  6  1 92
0    16 60.38 1906 112.37  16.00   0  0.00  59.95 1918 112.31   0 0  7  1 92
0    16 59.36 1863 108.01   0.00   0  0.00  60.00 1844 108.07   0 0  6  1 93
0    16 59.88 1933 113.05   0.00   0  0.00  60.40 1915 112.98   0 0  7  1 92