[Stgt-devel] Performance of SCST versus STGT

Erez Zilber erezz
Thu Jan 17 15:22:24 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:
>>>> Hello,
>>>> 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
> But I don't know about the details so let's wait for Pete to comment
> on this.
> Perhaps Voltaire people could comment on the tgt iSER performances.

We didn't run any real performance test with tgt, so I don't have
numbers yet. I know that Pete got ~900 MB/sec by hacking sgp_dd, so all
data was read/written to the same block (so it was all done in the
cache). Pete - am I right?

As already mentioned, he got that with IB SDR cards that are 10 Gb/sec
cards in theory (actual speed is ~900 MB/sec). With DDR cards (20
Gb/sec), you can get even more. I plan to test that in the near future.


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