[Stgt-devel] SCC vs SES

Mark Harvey markh794
Thu Jun 21 10:03:37 CEST 2007

Hello One and all.

Just brushing up on the recent changes to the stgt with regards to the 
SCC module.

The most recent draft doco at the T10 site I could locate is dated 12 
Sept 1997 (scc2r04.pdf)

 From my 10 minute read of these standards, the 'scc' device appears to 
be aimed at the RAID Disk array and fine grain control of disks within a 
RAID array (hot-swap spares, redirecting SCSI commands to a device 
within an array, etc).

While this model will suit the existing SBC / MMC modules, the SES (SCSI 
Enclosure Service) model would IMO be a better 'fit'.

i.e. The target 'owner' is an enclosure, rather than a SCSI Controller..

This way, the enclosure can be parent to all devices within the target.

Having the SES be the 'parent' for all LUN within the target, a SCC 
module could then become a LUN within the SES framework (if this 
functionality is required) to direct SCSI commands to the SBC/MMC type 
devices within the target.

The SES model would be a better fit with regards to virtual libraries. 
i.e. Each stgt target is an Enclosure with x number of logical units 
within the enclosure.

 From a practical point of view - As there is no SCC unique code behind 
the SCC target, both the SCC or SES models will work.

I could see potential issues where a (unknown / as yet untested) SCSI 
initiators finding a SCC controlling a set of LUNs which happened to be 
tape drives and/or medium changer may fail...

Thoughts ?

Mark Harvey

More information about the stgt mailing list