update:

for iscsi target i use these settings:

MaxRecvDataSegmentLength 262144
MaxBurstLength 16776192
MaxXmitDataSegmentLength 262144
firstBurstLength 65536
DataDigest None
MaxOutstandingR2T 8
InitialR2T No
ImmediateData yes
HeaderDigest None
Wthreads 8

after i change MaxXmitDataSegmentLength to default 262144 i can acces the targets from xen (using scst)

any suggestions?