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What iSCSI weaknesses should I consider when developing iSCSI services offerings?

iSCSI SAN storage is still developing and iSCSI storage may encounter growing pains.

What iSCSI weaknesses should you consider when developing iSCSI services offerings?
With all the hype and promise of iSCSI, there are still some caveats worth mentioning.
  1. IP networks often have higher latency than localized storage area networks (SANs). Fibre Channel (FC) networks were designed with a simple protocol and standards limit SAN size. This means that FC network latency is often measured in microseconds rather than milliseconds.
  2. We have more experience with FC SANs. iSCSI SAN storage is 5-10 years newer to market. It will have some growing pains.
  3. Mixing normal IP traffic with iSCSI storage traffic will degrade performance. In a nonprioritized or dedicated network, iSCSI packets must compete with email, Web and application traffic. The sensitive nature of block I/O requires that it be routed to its destination with the highest priority.
  4. Some operating systems still don't have native iSCSI SAN storage support. It is a cruel fact that legacy operating systems are still around. You can easily find NT 4.0, Novell Netware, AIX 4.3, Solaris 2.6 and HP/UX10.20 systems running important applications. None have iSCSI support.
  5. IP NICs put extra burden on server CPUs. In the world of 4 GHz processors, this may not be a big deal, but without TOE (TCP offload engines), the server CPU does all the work. On a Sun SPARC server, you will see 1-2 CPUs at 100% for each fully utilized Gigabit Ethernet port. FC host bus adapters (HBAs) do all that work for the server.
  6. iSCSI storage management tools are underdeveloped. This is really a function of iSCSI's newness to the market. Everybody is selling a storage resource management (SRM) tool to manage SAN storage, but few address iSCSI.
This was first published in January 2007

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