Off the back of a few posts Ive been reading recently, including Snigs post below on Brocade Oversubscription, I just thought Id sound off a little on the networking side of SANs.
I for one am no fan of ISLs. They are the bane of too many a storage admins life, at times mine included. But because most data centres are planned out on the back of a standard sized postage stamp, they are often a necessary evil just to keep things ticking over.
But I didn't always think like this. You see, way back (well its not that long ago actually but it sounds better this way) when I was first starting into Storage Area Networking I really liked the "networky" side of SANs. ISLs, trunk groups, trunk masters, name server merges….. you know, the type dark arts that brought us respect amongst out IT peers and drove rates up.
I'd previously done a bit of Cisco IP networking and because of that, I got on well with the network guys and we had a bit of Windows vs Unix type banter going. For example, I liked the fact that "my switches" (SAN switches) usually cost a lot more than the cheapex ones the network team bought. I also liked the way that frames absolutely screamed through my switches without touching the sides. Whereas the frames that passed through the network guys IP switches strolled in comparison, many of which stopped for a cup of tea on their way, and in fact some of them frequently went missing en route. Not mine though, no "missing frames adds" on the walls of my switches. But still, the network guys had one thing over me that I didn't like. Their networks were much bigger and complicated than mine, and their diagrams were so much more impressive than mine (back in those days "complicated" and "impressive" were the same thing, for me at least).
So I really liked the idea of connecting lots of switches into a single fabric (dual fabric design of course) and have the associated impressive (read complicated) diagrams hanging off the walls around my desk.
Fortunately those days are gone. Ive grown up a lot since then……. errr….well…… Anyway, these days simplicity is the key. Ive just seen too many irritating little problems with ISLs and bigs SANs. And troubleshooting SANs is just so damn annoying at times.
One thing that had a real influence on me was some work that I did for a telco company who have a policy of no ISLs in their SAN environments. A lot of people initially sniggle at the idea, and to be honest, I too raised an eyebrow when I first heard this. But I have to say that in their SAN environments problems were noticeably fewer and farther between, and when they did occur they were so much more limited in their scope and so much easier to troubleshoot.
Just off the top of my head the following lists some of the advantages that I see in smaller SANs, especially SAN islands –
Firmware upgrades are so much easier.
Other maintenance is much simpler
Troubleshooting is much simpler
Change Management people are far more comfortable with small SANs
Performance is better
Management and monitoring "can" be better in some ways
Sure, there are drawbacks, even with today's technologies. I just wonder how many of the future SAN related technologies, I'm thinking particularly services, are going to be geared around larger interconnected fabrics and networks? Methinks that the SAN is no longer merely an interconnect, and that ISLs and the other dark arts mentioned above will still be plaguing us in the years to come.
Feel free to educate me.