scsi-target and the buffer cache

[Eric Anderson]

Nate Lawson wrote:
> [mailing list changed to scsi@]
>
> Eric Anderson wrote:
>> Nate Lawson wrote:
>>> Scott Long wrote:
>>>> Eric Anderson wrote:
>>>>
>>>>> Nate Lawson wrote:
>>>>>> Agree 100%.  While having it in usermode means there are boundary 
>>>>>> crossings that increase per-transaction latency, the actual bulk 
>>>>>> data transfer is via zero-copy IO and you should be able to 
>>>>>> exceed the data transfer rates of several 10K RPM drives on 
>>>>>> decent hardware.
>>>>>
>>>>> Ok, great.. Now, will scsi_target work ok with raw devices, or 
>>>>> only files?  (although I'm not sure theres all that much 
>>>>> difference really).
>>>>>
>>>>
>>>> You can write your userland code to use whatever files or devices you
>>>> want.  Are you talking about the scs_target.c code in
>>>> /usr/share/examples?  That's just a skeletal example that you can use
>>>> as a starting point for your own work.
>>>
>>> No, it's not just a skeletal example.  You can point it at a raw 
>>> device as the backing store file and it will work as a block device 
>>> (i.e. RBC command set).  It has been tested as working at least 
>>> moderately fast over SCSI, FC, and firewire.
>>>
>>
>> I'm finally getting around to playing with this, and I'm having some 
>> problems.  First, I can't seem to make one isp card in target mode 
>> and the other an initiator.  I've messed with adding the following to 
>> loader.conf:
>>
>> hint.isp.0.role="initiator"
>> hint.isp.1.role="target"
>>
>> that still doesn't show my currently connected fiber channel devices 
>> on the initiator side.
>>
>> I've tried a few different kernel options, currently I have:
>>
>> options         ISP_TARGET_MODE=1
>> device          targ
>>
>> I've also tried just:
>>
>> options         ISP_TARGET_MODE
>>
>> and that doesn't seem to allow me to select one either.
>
> hints aren't needed.  Here's an intro on how to use it:
> http://root.org/~nate/freebsd/scsi/README.targ
>
> The same card is in target or initiator mode based on the scsi_target 
> user program.  When it's running, target mode is enabled.

Hmm.  Then shouldn't a

camcontrol rescan all
camcontrol devlist -v

show me all the devices on the FC network?  If I remove the target mode 
stuff out, and do that, I see all my devices.  With it in, I see no 
devices. 

When I run the scsi_target tool (scsi_target -d 0:3:0 /mnt/testfile), it 
shows a bunch of "sending ccb (0x332)" and (0x334) messages alternating 
for a couple hundred lines, then "main loop beginning" and a few other 
messages.  If you want the full details, I'd be glad to sent them.

Once scsi_target is running, my other FC initiator (FreeBSD 6.1- also) 
can see it. 



>
>> Anyhow, I've compiled scsi_target (from 
>> /usr/share/examples/scsi_target), and tried to run it using a 20gb 
>> file as the target, and still I can't seem to get it working.
>> Is there a doc somewhere I need to read?
>>
>> Also - as a side note, the Makefile for scsi_target seems like it's 
>> missing a path variable in order to do a make install, but that's not 
>> a real issue.
>
> There was some debate when I imported it whether to make it an example 
> or usr.sbin.  Given the lack of updates (i.e. ki_sig or whatever), I 
> probably should have put it somewhere else.

Is it a totally non-supported kind of tool?  Is there another option for 
scsi target mode?


Thanks!
Eric


-- 
------------------------------------------------------------------------
Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
------------------------------------------------------------------------