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

ronnie sahlberg ronniesahlberg
Fri Jul 25 22:30:09 CEST 2008

While it wont explain the drop from 55-44Mbyte/second
I think ~50MByte/second is pretty good considering such a latency-bound
test such as single threaded dd writing one 1024byte block at a time.

I would either run dd with a much much larger blocksize, or with many
concurrent dd in parallell
in order to reduce the cost-per-byte-in-latency to get throughput
numbers instead of latency-bound numbers.

On Sat, Jul 26, 2008 at 4:46 AM, Richard Sharpe
<realrichardsharpe at gmail.com> wrote:
> On Wed, Jul 2, 2008 at 2:01 PM, Richard Sharpe
> <realrichardsharpe at gmail.com> wrote:
>> Hi,
>> 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).
> OK, I have shifted to faster machines (a couple of 1U Tyan B5211s with
> Quad core Xeon X3230  @ 2.66GHz and jumbo frames ...)
> I get around 58.6MB/s with 819MB but it drops to 44-45MB/s with 8GB
> files (with a variety of block sizes (4096, 8192, 16384).
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