[Stgt-devel] A curious observation with iSCSI and SCSI tgt ...

Richard Sharpe realrichardsharpe
Wed Jul 2 23:01:02 CEST 2008


I am testing some configurations I have laying around here at work while
waiting for our new hardware to arrive.

I set up one system, a 1U with 2GB of memory and a Xeon (speed not really
relevant to this) and GigE as a target and set up a virtual disk via iSCSI.

Then on another system, an old DELL, I set up the initiator, and ran:

   dd if=/dev/zero of=/dev/sda1 bs=1024 count=1000000

and I got a throughput of 10.5-10.8MB/a while consuming around 10-12% of the
CPU on the target (shown via top).

That number looked suspiciously like 100BaseT numbers to me, and lspci told
me it was.

So, I shifted to another system with GigE and did the same tests. This time
around, tgtd on the target machine was getting 25-30% with spikes up to 99%
but the throughput stayed around 10.2MB/s.

I am going to pull down the kernel profiling tool to see what is going on,
but I wonder if anyone else knows off the top of their heads?
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