Re: question on iSCSI and NBD

[Andre Hedrick <andre@linux-ide.org>]

Hi Sunzen,

NBD is not an accepted industry standard nor has it ever been put forward
as a serious means of SAN.  NBD totally lacks the ablity to address the
requirements of Enterprise SAN customers.  There is no means to issue or
handle task management.  IE NBD can not manage its way out of corruption
or transport failure or migration.  It is a UNIX limited transport and
totally lacks a serious approach to addressing the needs or requirements
for "Enterprise".  People pay for "Enterprise" because their data is worth
more than the hardware or protocol carring the information.

Enterprise has invested in management suites like Veritas, Legato, IBM.
EMC, MacData, Brocade, Cisco, and the new comers to SAN like Wasabi,
StoneFLY, BlueArch, Intransa, and my company PyX Technologies.

iSCSI is a means of supporting all the current administative tools today.

NBD totally lacks and will never have the ability to easily managed in the
marketspace.  NDB is not iSCSI.  NBD is not Enterprise SAN.  NBD is not a
serious solution for SAN.  NBD will not be adopted as SAN.

NBD is useful in its free and opensource environment.
NBD is a great undergraduate project to learn about SAN.

Take it from an opensource old hat, NBD is not in the same arena or class
of iSCSI SAN.  NBD relies on the simple and weak tcp-crc.  It does not
support real storage data integrity transport tests.

iSCSI supports command and data CRC32C integrity checks.

Any deployment of iSCSI without CRC32C is in the same class of NBD.
This CRC32C is identical to the one used in pSCSI and pATA between the
HOST(chipset) and the DEVICE(drive).  If you think you can disable the ECC
on the real spindle media and expect data to maintain integrity, reload
your crack pipe and inhale.

NBD is filesystem depended for the most part, as it has to be mounted to
be usable, iirc.  There is not a state machine protocol one could issue to
talk to the raw device discretely.  All NBD has is the basics of
open,read,write,close.  iSCSI has SCSI-Taskfile and/or Bus-Phase Command
operations.  This is the key difference, a communication pathway which is
standardized and utilizied by the promoters, leaders, and creators in the
storage industry.

Moving on to the issues of ACL's, where are they in NBD?
Moving on to the issues of Security, where are they in NBD?
Moving on to the issues of interoperability, where are they in NBD?
Moving on to the issues of standardization, where are they in NBD?

The list goes on, and on ...

Again NBD is a nice idea and works in some environments.
It can be viewed as poor-man's san, but until adopted and promoted by
individuals, groups, companies who will push for standardization ...

Well no need to dig the hole any deeper for NBD.

Cheers,

Andre Hedrick
LAD Storage Consulting Group
http://www.pyxtechnologies.com/

PS If there is something I do not understand or missed about NBD, please
send a correction.

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. 
> 
> 
> 
>