Date: Thu, 10 Apr 2003 11:40:12 -0700 (PDT)
From: Andre Hedrick <andre@linux-ide.org>
To: "sunzen.w" <wangxz@ict.ac.cn>
cc: ips@ece.cmu.edu
Subject: Part II (Re: question on iSCSI and NBD)
In-Reply-To: <1049939394.1053.52.camel@sunzen>
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Hi Sunzen,

I did not address the other points ypu put forward in the previous reply.

One of the key issues nobody wants to address, everything about storage is
a lie.  iSCSI does a fantastic job of doing it bold and in your face.
Now, what do I mean by stating "Everything about Storage is a Lie"?

Given when a host talks to device, the device tells the host what it wants
the host to know about itself and not everything is disclosed.  This is
similar to the usage of virtual devices like LVM, RAID, or any other
non-scsi spindle/media.  iSCSI is perfect for keying the storefornt of
storage in the same information path, and it even does it better than in
the past.

Now any quality version of iSCSI targets in the market space will be able
to mimic or lie about its physical spindle, and report it as a SCSI
device.  This somewhat follows the history of MicroSoft's MiniPort(tm)
API or in the BSD's aka CAM.  Believe it or not the miniport is slicker
and smoother than CAM.

So when one exploits the virtual devices and converts their appearance and
behavior to a scsi-like device, one also gains the ability to use the
known and trusted management suites.  I do not use or hold any trust in
their features, but my customers and others do.

Lastly iSCSI has to power to democratize storage and strip away from the
giant sloaths, who tightly control FC and fail at the interoperability
test, to empower the customers of today bound in the chains of FC.  While
the greatest market space is for the 95% of the ignored customer base who
can not or refuse to pay the excessive costs of FC.  Key point is that an
emerging technology does not replace an existing one out of the box;
however, it does provide a way and an out for todays customers of
enterprise and future customers who want cost effective enterprise.

Given storage is a customer driven marketspace, NBD has no customers.

The only other item left is the 5 paradigm shift in the economy which will
accelerate the adoption and migration to iSCSI, but that is another email
offline for you to enjoy later.

Cheers,

Andre Hedrick
LAD Storage Consulting Group
http://www.pyxtechnologies.com/

All trademarks belong to their respective companies.

On 10 Apr 2003, sunzen.w wrote:

> I have a question on iSCSI.It is originated from contrast of iSCSI with
> NBD.
> 
> As all know, NBD also support block storage over IP. So maybe we can
> also consider it as a technology of IP storage,which originated even
> earlier than iSCSI.
> 
> Besides it's simplicity (which may bring less powfulness. ?)
> Another feature i think more is that it intercepts on the request level.
> while iSCSI intercepts on more lower level,it is on SCSI command level.
> This shows a different computing distribution strategy.
> 
> But with the prevalence of virtual device(such as LVM ,...)
> what are the results of the two different technology?
> In order to access the virtual device, the low level request of SCSI
> command which are carried by iSCSI should be transformed to upper level
> request,while the additional transformation is not needed when using
> NBD,where just a simple routing mechanism is needed. 
> 
> Do i understand them correctly?
> As a technology of IP storage ,iSCSI provide apparent advantages(not all
> the aspects) over FCP 
> What advantages over NBD does iSCSI provide?  
> 
> need all your point and help.
> 
> with my best regards. 
> 
> 
> 
>