[Stgt-devel] Performance of SCST versus STGT

Vladislav Bolkhovitin vst
Thu Jan 17 11:34:46 CET 2008

FUJITA Tomonori wrote:
> On Thu, 17 Jan 2008 12:48:28 +0300
> Vladislav Bolkhovitin <vst at vlnb.net> wrote:
>>FUJITA Tomonori wrote:
>>>On Thu, 17 Jan 2008 10:27:08 +0100
>>>"Bart Van Assche" <bart.vanassche at gmail.com> wrote:
>>>>I have performed a test to compare the performance of SCST and STGT.
>>>>Apparently the SCST target implementation performed far better than
>>>>the STGT target implementation. This makes me wonder whether this is
>>>>due to the design of SCST or whether STGT's performance can be
>>>>improved to the level of SCST ?
>>>>Test performed: read 2 GB of data in blocks of 1 MB from a target (hot
>>>>cache -- no disk reads were performed, all reads were from the cache).
>>>>Test command: time dd if=/dev/sde of=/dev/null bs=1M count=2000
>>>>                             STGT read             SCST read
>>>>                          performance (MB/s)   performance (MB/s)
>>>>Ethernet (1 Gb/s network)        77                    89
>>>>IPoIB (8 Gb/s network)           82                   229
>>>>SRP (8 Gb/s network)            N/A                   600
>>>>iSER (8 Gb/s network)            80                   N/A
>>>>These results show that SCST uses the InfiniBand network very well
>>>>(effectivity of about 88% via SRP), but that the current STGT version
>>>>is unable to transfer data faster than 82 MB/s. Does this mean that
>>>>there is a severe bottleneck  present in the current STGT
>>>>implementation ?
>>>I don't know about the details but Pete said that he can achieve more
>>>than 900MB/s read performance with tgt iSER target using ramdisk.
>>>http://www.mail-archive.com/stgt-devel at lists.berlios.de/msg00004.html
>>Please don't confuse multithreaded latency insensitive workload with 
>>single threaded, hence latency sensitive one.
> Seems that he can get good performance with single threaded workload:
> http://www.osc.edu/~pw/papers/wyckoff-iser-snapi07-talk.pdf

Hmm, I can't find which IB hardware did he use and it's declared Gbps 
speed. He declared only "Mellanox 4X SDR, switch". What does it mean?

> But I don't know about the details so let's wait for Pete to comment
> on this.

I added him on CC

> Perhaps Voltaire people could comment on the tgt iSER performances.

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