[Stgt-devel] Adding Virtial Tape & Changer targets

[Mark Harvey]

On 3/21/07, Douglas Gilbert <dougg at torque.net> wrote:
>
> Mark Harvey wrote:
> > A quick introduction.
> >
> > I am planning on adding support to the stgt for both SSC and SMC
> > devices with the aim of full Virtual Tape Library support.
> >
> > I have a working VTL based around the scsi_debug kernel module +
> > char-device 'back-end' to pass SCSI commands thru to user-space
> > daemons (which poll the char device looking for work to do). These
> > daemons act as the SSC or SMC devices.
> >
> > This VTL I have had working for over 12mths.
> >
> > However there are some limitations (like a kernel module required for
> > each OS port).
> >
> > I want to move this code base across to an iSCSI frame-work and have
> > finally given up on the Intel iSCSI Reference code base.
> >
> > There are some aspects of the stgt code that I would like to modify to
> > make this 'port' a little easier.
> >
> > There is a lack of a 'generic' pointer for any data structures used
> > for each target.
> > i.e. I would like to malloc() required storage space to keep MODE/LOG
> > SENSE data per target.
>
> Mark,
> Do you need to implement MODE SELECT? It isn't in stgt
> or any other command that has metadata to be parsed
> in the data_out buffer.
>
> As far as I can see that needs a "double parse". The
> first time with the cdb alone so the parser can
> work out the allocation length. That length is them
> passed back to the transport which fetches a data_out
> buffer of that size from the initiator. Then the
> transport needs to revisit the parser, this time
> with cdb+data_out.
>
>
> Doug Gilbert
>

Hi Doug,

Both MODE SELECT/MODE SENSE and LOG SELECT/LOG SENSE commands are used by
NetBackup (Which I support for a living - and the main force behind writing
the VTL).

Although, NetBackup really only uses the MODE SELECT to place the tape
device into variable block mode, so limited support will be OK. (i.e. The
block-descriptor block)

There are also a few 16byte CDB commands (READ / WRITE ATTRIBUTE) used by
the latest version of NetBackup which I also would like to implement.
Certainly the WRITE ATTRIBUTE would fit your description of metadata in the
data_out phase.

Cheers
Mark
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