Re: Re[2]: ata over ethernet question

[Dmitry Yusupov]

On Thu, 2005-05-12 at 14:52 -0400, James Bottomley wrote:
> On Wed, 2005-05-11 at 00:00 +0200, Guennadi Liakhovetski wrote:
> > A follow up question - I recently used nbd to access a CD-ROM. It worked 
> > nice, but, I had to read in 7 CDs, so, each time I had to replace a CD, I 
> > had to stop the client, the server, then replace the CD, re-start the 
> > server, re-start the client... I thought about extending NBD to (better) 
> > support removable media, but then you start thinking about all those 
> > features that your local block device has that don't get exported over 
> > NBD...
> 
> That's correct; NBD is basically just a remote data pipe type block
> device.  It doesn't understand arbitrary packet commands.
> 
> > Now, my understanding (sorry, without looking at any docs - yet) is, that 
> > iSCSI is (or at least should be) free from these limitations. So, does it 
> > make any sense at all extending NBD or just switch to iSCSI? Should NBD be 
> > just kept simple as it is or would it be completely superseeded by iSCSI, 
> > or is there still something that NBD does that iSCSI wouldn't (easily) do?
> 
> Caveat: I've done quite a bit of work on nbd, so I'm biased.  However,
> for what it does, nbd is extremely small, simple and efficient, so I
> think we'd want a hole in our head to replace it with something as
> complex and bloated as iSCSI---remember we'd need both a target and an
> initiator to do what nbd does today.

oh, please! don't compare nbd and iSCSI this way...
iSCSI is an emerging SAN technology, and the only technology to compare
is FC.

> However, there is room for improvement in nbd, notably the handling of
> packet commands, which looks to be eminently doable in the current
> infrastructure (this would basically make nbd a replicator for the linux
> block system, and would probably necessitate some client side changes to
> achieve).  If you have any thoughts in this direction, you could drop an
> email to the maintainer.
> 
> James
> 
> 
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