[BBLISA] iSCSI - opinions / experiences?

[Adam S. Moskowitz]

"Eddy Harvey" <bblisa2 at nedharvey.com> wrote:
> SAN is faster and better, but more expensive.

We could debate which is faster and why but let's not.

I will, however, argue with "better": NAS and SAN -- or more correctly,
file sharing versus block access -- serve two different purposes and
most often solve different problems. If your requirement is to give
multiple hosts read/write access to the same file while preserving
locking semantics and the like, block access is almost certainly worse
than file access and, in particular, than a file *sharing* protocol such
as NFS or CIFS.

> . . . in my personal experience, nfs has a tendency to hang up the system
> whenever there's a network outage or you reboot the nfs server. You don't
> have that problem with SAN, because the network is more reliable and there
> is no nfs server.

I will match my NetApp NFS server against any SAN box and show you as
good if not better numbers for speed and reliability. I will also match
my high-end Cisco plain old Ethernet switch against any Fiber Channel
switch for reliability and again get as good if not better numbers.

As for hanging the system, well, NFS might or might not hang but the
system won't necessarily crash. When you SAN switch or network dies,
it's like ripping the system disk out from under a running system -- you
*will* crash.

My point is that, in general, reliability is far more about what
hardware you choose and how you connect it up than the protocol and/or
access method the hardware provides.

> More Expensive: I normally expect a SAN to cost at least 3 times more
> than NAS of the same size.

While I will be the first to admit that a NFS setup from NetApp is one
of the most expensive you can find, it's often less that "equivalent"
SAN set-ups. But the great thing is that same hardware can provide SAN
service, too (at the same time, no less), so you can build a very
reliable SAN for roughly the same cost as a NAS set-up. Well, provided
you use iSCSI and not FC, 'cause FC switches are always gonna drive the
cost up.

AdamM