[BBLISA] iSCSI - opinions / experiences?

[Adam S. Moskowitz]

Daniel Feenberg <feenberg at nber.org> asked:
> OK, but how do I use a SAN to replace NFS?

and "A. Rich" <arr at oceanwave.com> replied:
> You either set up some sort of active-active clustering amongst your machines,
> or you have one (possibly set of) designated server that mounts the SAN then
> exports it out to the rest of your hosts via CIFS, NFS, AFS, whatever.

I'd like to suggest the following, to avoid confusion . . .

Rather than saying "SAN" and "NAS," say "block access" and "file
sharing."

Block access and file sharing are two different technologies that solve
different problems. Yes, both problems involve hosts and disks, but
ignore that for now.

If you want to give multiple hosts simultaneous access to one or more
files then you need something like NFS or CIFS or a clustered file-
system.

If you want to give multiple hosts access to different parts of the same
(logical or physical) disk then you need something like iSCSI or
whatever the correct-for-this-situation name of FC is (both of which are
based on SCSI).

Now, it's entirely likely that a solution to your file sharing problem
will include a block access mechanism (just like Amy described above),
but in most cases SANs and NASes are not interchangeable.

I think I said this before, but I think it bears repeating: iSCSI and
the like (i.e., "SAN") is functionally just a really long cable between
the CPU and the disk; NAS is one computer acting as a gatekeeper for
lots of computers trying to access the same file(s). Yes, this is an
over-simplification, but when trying to remember what each technology
does best it's a reasonable working model.

AdamM