RAID5 write speed from VmWare ESXi

[gintonic]

Hi!
I created software raid5 of 5 SATA HDD on Intel SR2500ALBRP with 12Gb RAM server.
Create iSCSi target for my ESXi host. Use VM Win2003SrvStdx64 for testing performance and i see that write speed is very slow - 70 IO/s or 0.5 mb/s but read speed 14000 IO/s and 105 mb/s.
What can i do that increase write speed?

[gintonic]

sqlio v1.5.SG
using system counter for latency timings, -1800967296 counts per second
parameter file used: param.txt
file e:\testfile.dat with 2 threads (0-1) using mask 0x0 (0)
2 threads writing for 360 secs to file e:\testfile.dat
using 8KB random IOs
enabling multiple I/Os per thread with 8 outstanding
size of file e:\testfile.dat needs to be: 4194304000 bytes
current file size: 0 bytes
need to expand by: 4194304000 bytes
expanding e:\testfile.dat ... done.
using specified size: 4000 MB for file: e:\testfile.dat
initialization done
CUMULATIVE DATA:
throughput metrics:
IOs/sec: 71.62
MBs/sec: 0.55
latency metrics:
Min_Latency(ms): 72
Avg_Latency(ms): 222
Max_Latency(ms): 771
histogram:
ms: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24+
%: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 100