[Stgt-devel] [Iscsitarget-devel] Re: stgt a new version of iscsi target?

Mike Christie michaelc at cs.wisc.edu
Wed Dec 14 20:55:53 CET 2005

Vladislav Bolkhovitin wrote:
> Mike Christie wrote:
>>> Are you sure that there are no now or will be available in the 
>>> nearest feature such (eg iSCSI) SCSI arrays with response 
>>> time/latency so small that having 5 (five) context switches or more 
>>> per command, some of which include map/unmap operations, will not 
>>> increase the latency too much? I mean, eg NFS server, which 
>>> originally was user space daemon and many people didn't want it in 
>>> the kernel. Eventually, it's in. I don't see any fundamental 
>>> difference between NFS server and SCSI target server, 
>> Isn't the reason a NFS server is still in the kernel is becuase some 
>> of the locking difficulties?
> Might be. But from what I remember, the major reason was the 
> performance. After googling a bit I found many acknowledgments of that.

I do not think we are going to get anywhere with this type of thread :(

We should try to compare at least one of the userspace *nbd 
implementations with the unh target in scst. I see some that just do 
some basic socket ops (no sendfile type hook in even) for the network 
part then just async or normal read/writes. I do not want to comapre FC 
to nbd, but maybe comparing software iscsi to userspace nbd is a little 
more fair. I think ata over ethernet has a userspace target too. Is the 
unh target defaults set ok for performance testing, or could you send 
some off list, so we can at least test those.

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