[Stgt-devel] [Scst-devel] Performance of SCST versus STGT

Vladislav Bolkhovitin vst
Thu Jan 17 14:44:31 CET 2008

Robin Humble wrote:
> On Thu, Jan 17, 2008 at 01:34:46PM +0300, Vladislav Bolkhovitin wrote:
>>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?
> SDR is 10Gbit carrier, at most about  ~900MB/s data rate.
> DDR is 20Gbit carrier, at most about ~1400MB/s data rate.

Thanks. Then the single threaded rate with one outstanding command 
between SCST SRP on 8Gbps link vs STGT iSRP on 10Gbps link (according to 
that paper) is 600MB/s vs ~480MB/s (page 26). Still SCST based target is 
about 60% faster.

> On Thu, 17 Jan 2008 10:27:08 +0100 "Bart Van Assche" <bart.vanassche at gmail.com> wrote:
>>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                                                                                                                    
> it kinda looks to me like the tgt iSER tests were waaay too slow to be
> using RDMA :-/
> I use tgt to get 500MB/s writes over iSER DDR IB to real files (not
> ramdisk). Reads are a little slower, but that changes a bit with distro
> vs. mainline kernels.

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