iotop for iSCSI or zfs datasets

[Eugene M. Zheganin]

Hello,


I have several iSCSI SAN systems running FreeBSD, and I need a tool to 
quickly determine which target/targets (and thus which initiator) are 
consuming most of iops. I can see that there are cfiscsi/iscsi probes in 
the FDT provider, and lots of zfs probes. Since my targets are using 
zvols as backends, both types will fir. I have some basic skills with 
dtrace, but in this case I totally lack documentation, so could you 
please point me to a direction (I'm not quite good at reading sources, 
but if that's the only way - you could point me to a specific part of 
the FreeBSD source tree I guess) to find the answer to a question "where 
can I find which probes/functions can I use to gather this data, 
including the argument list/types for them?"

I was made aware that there's a ctlstat(8) utility, but it's not handy 
when it comes to hundreds of LUNs.

I also can see the iotop in the context of network data transferred 
using trafshow, but this doesn't scale well to iops, and I would see 
reads/writes per second in terms that block devices use.


Thanks.

Eugene.