RE: iSCSI: Re: iSCSI & Linked Commands

["Douglas Otis" <dotis@sanlight.net>]

Robert,

You are correct in the explicit definitions of the SAMS dictionary.  I was
simply attempting to explain the reason for a concern about sequential
ordering as it relates to these two devices.  Perhaps they could add
nextitive addressing.  :)

Doug

> -----Original Message-----
> From: Robert Snively [mailto:rsnively@brocade.com]
> Sent: Monday, April 30, 2001 4:13 AM
> To: Douglas Otis; Robert Snively; Stephen Bailey; ips@ece.cmu.edu
> Subject: RE: iSCSI: Re: iSCSI & Linked Commands
>
>
> Doug,
>
> Sorry, that is not how the SCSI standards define relative
> addressing.  Relative addressing is a displacement from the
> last logical block transferred in an SCB read or write command
> and applies to the read or write command in which the RELADR
> bit is set.
>
> Tape devices have the property of sequential access.  Except
> for Locate (which is an absolute address), all tape addressing
> is "next".  To get to "next + n", you have to do a separate
> explicit command to step across the intervening blocks, which
> are not logical blocks and cannot be directly addressed.
>
> It may be that you are applying generic English definitions to
> words which SCSI has assigned a special meaning.
>
> Bob
>
> >  -----Original Message-----
> >  From: Douglas Otis [mailto:dotis@sanlight.net]
> >  Sent: Thursday, April 26, 2001 10:15 AM
> >  To: Robert Snively; Stephen Bailey; ips@ece.cmu.edu
> >  Subject: RE: iSCSI: Re: iSCSI & Linked Commands
> >
> >
> >  Robert,
> >
> >  Relative addressing is not defined because that is the only means of
> >  addressing.  Relative to the last block.
> >
> >  Doug
> >
> >
> >  > Doug,
> >  >
> >  > Relative addressing is not defined in the SSC command set nor
> >  > in the SPC command set for tapes.
> >  >
> >  > Bob
> >  >
> >  > >  -----Original Message-----
> >  > >  From: Douglas Otis [mailto:dotis@sanlight.net]
> >  > >  Sent: Monday, April 23, 2001 9:36 AM
> >  > >  To: Stephen Bailey; ips@ece.cmu.edu
> >  > >  Subject: RE: iSCSI: Re: iSCSI & Linked Commands
> >  > >
> >  > >
> >  > >  Stephen,
> >  > >
> >  > >  Unlike random access devices, sequential access devices
> >  operate with
> >  > >  relative addressing.  For random access devices, this is a
> >  > >  seldom used
> >  > >  option.  There is a requirement to bind commands together to
> >  > >  ensure order of
> >  > >  execution on these devices.  By popular, you mean not
> >  sequential?
> >  > >
> >  > >  Doug
> >  > >
> >  > >
> >  > >  > Julian,
> >  > >  >
> >  > >  > > According to your logic no FCP implementation can use
> >  > >  linked commands?
> >  > >  > > Is this true for all OS's?  Is it a verified fact
> >  or foloklor?
> >  > >  >
> >  > >  > In my experience it's fact.  I have never used a SCSI
> >  > >  stack which both
> >  > >  > supported AND used linked commands.  Like some others
> >  > >  here, I always
> >  > >  > assumed AIX might :^) Ralph has pointed out that T10
> >  is well aware
> >  > >  > that the feature is not popular.  There are other ways of
> >  > >  > accomplishing the same thing that are less likely to blow
> >  > >  up in your
> >  > >  > face.
> >  > >  >
> >  > >  > > Is it so also for the new MS StorPort driver?
> >  > >  >
> >  > >  > I don't know, but I'd be really surprised if they did
> >  use linked
> >  > >  > commands.  You have to be pretty nuts to rely on a feature
> >  > >  that's not
> >  > >  > even exercised by most SCSI implementations.
> >  > >  >
> >  > >  > Steph
> >  > >  >
> >  > >
> >  > >
> >  >
> >
> >
>