[stgt] [PATCH] sg-based backing store

[Doron Shoham]

Alexander Nezhinsky wrote:
> Backing store based on SCSI Generic driver (sg), v.3.
> allows to route scsi commands to the native scsi devices
> unchanged. It uses Direct I/O (dio) to avoid memcopy
> to the buffer cache.
> 
> Using sg allows asynchronous execution, commands are 
> written to a sg-backed char device, completions are
> read from the same device, which can be polled 
> asynchronously.
> 
> This bs provides significant performance improvement when 
> working with native scsi devices. In a setup, where 
> the scsi devices are exported by a tgt with bs_null,
> and both links (from initiator to target and from the 
> target to the "backing-store" target) are iSER/IB
> sustained bandwidth of 1450 MB/s for READ and
> 1350 MB/s for WRITE is achieved. This to be compared to
> 700-800 MB/s when running with bs_rdwr in the same setup.
> Some improvements are seen with IOPS as well:
> 60 kIOPS for READ, 38 kIOPS for WRITE
> (compared to 31/35KIOPS with bs_rdwr).
> 

Hi,

I applied this patch and it works, but I noticed that the serial number
reported by the device (using sg_inq) returned 'beaf11' instead of the real physical serial number.

Does it mean that the inquiry command is not transferred to the device and handled internally?

Thanks,
Doron

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