Object oriented issues

hafner at almaden.ibm.com hafner at almaden.ibm.com
Wed Aug 16 09:32:04 PDT 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* hafner at almaden.ibm.com
*


Dave,

I started to write a very long winded reply to some of your comments, but I
think they are getting repetitive.

However, let me try to summarize what I think are our philosophical
differences and then summarize my position.

1) I look at an OSD as a simplified NFS, not a glorified disk drive.  You
look at it the other way around.
2) As a simplified NFS, TCP/IP is the natural protocol.  As a glorified
disk, SCSI is the natural one.

I don't deny that a SCSI specification and implementation is possible.  I
just think that it would have enormous barriers to timely standardization
and (more importantly) to pratical deployment.
TCP/IP has no fundamental architectural limitations; SCSI has many.
SCSI *might* be changed, but that will take time (both in the standards
process and in deployment of the infrastructures required to implement the
standard).
SCSI has a lot of excess baggage that isn't needed for a clean OSD model
(mode pages, to name just one).

Additionally, I don't see any point in SCSI's favor over TCP/IP in either
the short or long term .

You wrote:
> I hope that I am willing as you to be convinced otherwise.
In fact, I don't really need to be convinced at all.  There are many things
that this industry is doing that I personally am agnostic about.  If some
things are going to happen anyway and I have opinions on "implementation",
then I'll speak up.  In other words, I'll stick my nose into anything with
an opinion, but I won't try to stop anything either.  (So, if you, et al,
want to push this through T10, I'll be willing to help, even if I think
you'd be better suited to push this elsewhere.  You'll notice that I didn't
make a big deal about this point in my talk at the T10 meeting, just raised
the banner.)

>I also think your list of open issues is worthwhile.  Would be willing to
>present a summary of your paper and your position on the protocol at the
>OBSD working group meeting?
I think I can be persuaded.  Do I need to do anything in particular to get
on the agenda?

>On the question of whether an OBSD is a disc drive, I fell pretty strongly
>that it is, and I will try to line up somebody to address this at the WG
>meeting.  (It turns out that there is a lot outside of OBSD that relates
to
>this particular subject.)
If you're talking about packaging an OSD in something that looks like a
disk drive, that's not really the point.  The point is more how it will get
used.  An OSD's real value over a block storage device (aka disk) is in
sharing among many hosts.  That implies a network attachment.  That means
(today), two primary choices, FC (and so SCSI over FC) or ethernet (and so
IP or TCP/IP).  The physical dimensions are less important to me than the
fact that on OSD is a networked device!  Now we need to decide what's the
best network to use!

[.. deleted the rest of the history...]

Jim Hafner


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