I very often get email questions about SAN vs. iSCSI.Â It’s funny that earlier, within minutes of completing a post on another site on the subject, I got queried in email about it.Â
I don’t see iSCSI making great inroads because it’s limited by the limitations of IP, that being that IP is a connectionless protocol that doesn’t guarantee delivery of packets at all, let alone in-order delivery.Â (FC doesn’t guarantee in-order delivery, but instead assembles the packets in order on receipt)
also, I think it’s universal that no one wants to put your storage traffic and your user traffic on the same network, especially since to date, Gigabit is it.Â Â Think about it.Â You request data from a client, the request is sent to the server, which then pulls the information across the same network from another server or iSCSI appliance, (such as NetApp or Clariion) and then sent back to the client over the SAME NETWORK.
That’s 3-4 times the network traffic.
Unless you’re going to have dedicated networks for storage and IP, it doesn’t make much sense.Â You’re still doubling your investment.Â Now granted with iSCSI you probably don’t need a dedicated SAN person (gasp, I might be out of a job soon!) but you do double the load on yourÂ network admins.Â (and they are a fiesty sort who don’t like having extra work heaped on them)
Though I’m guessing in the long run, when Ethernet reaches 10Gbit, it will bring the total cost down quite a lot, but by then fibrechannel will be so much the mainstream that it won’t matter.
I am surprised that in all my installs I’ve not seen more people using the IP over fibrechannel options that the full port drives offer.Â If you could run IP over a 2gig fibre link, say for dedicated backup purposes, wouldn’t that make a lot more sense?Â Especially since it seems that would free up the extra gigabit interface that comes on most servers for load-balancing and failover of network connections.
I alpha-tested some of the first iSCSI drivers in 2000, and didnt find them to be stable (or worthwhile) but then again, that was before the protocol was really refined.Â In the interest of fairness I should probably revisit it.Â Especially since we bought the iSCSI license on our Celerra. :)Â
I’m going to do something I’ve not done yet – I’d like to ask for comments on the subject.Â As highly as I do think of myself, I don’t pretend to know everything.Â If iSCSI is proving itself out I’d like to know, as I’ll re-evaluate my stance on it.