Pure IP SANs are here

You've probably heard the news: IP-based SAN solutions offered at a price of only cents per MB are entering the storage arena. If your budget is tight, for your next storage-purchasing campaign take a look at the different but equally interesting solutions from companies such as EqualLogic, Intransa, or LeftHand Networks.

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Who should be interested in iSCSI-based SANs? In theory every datacenter, but the most likely candidates are companies that still have internal or external storage arrays directly attached to their application servers. According to some estimates, 40 to 50 percent of the companies still use direct-attached storage: a potential gold mine for the pioneers of IP SAN.

The numerous benefits of moving from DAS (direct attached storage) to a SAN apply also to IP-based networks. After the initial setup most storage management activities won't affect running applications, storage becomes a centralized asset rather than a discrete resource on each server, and, perhaps most important, with the SAN you acquire also management software that provides more flexibility for critical tasks such as allocating storage to servers, monitoring performance, recovering from hardware failures, creating mirrors and snapshots, and adding more capacity.

In lay terms this means that from a central pool of storage you can carve volumes that attach to your servers over an Ethernet connection, preferably via a GbE switch that can handle jumbo (larger than 1500 bytes) frames.

In most cases, just installing an iSCSI driver on your Linux or Microsoft Windows server will turn your NIC (network interface card) into a storage-provisioning medium: You connect to the storage array management software, select the proper volume, and then turn it over to the usual volume management tools of your OS.

However, if you plan to move plenty of data between servers and volumes across those GbE links, you may have to install iSCSI HBAs (host bus adapter), which are slightly more expensive than plain NICs but have on-board chips that save your servers a significant amount of CPU cycles. As we all know, the TCP (terminal control program) protocol is a processor resources hog.

Will those DAS-bound companies (and others) buy IP SANs en masse reserving Fibre Channel-based solutions for a high-end niche? Only time will tell. The usual criteria of interoperability, scalability, performance, and reliability apply, but let's note that provisioning is only one aspect of the ultra complex storage puzzle.

Creating a snapshot or mirroring a volume for a host is a relatively easy task, but ensuring that the data content stays consistent requires close interaction with a variety of host applications including databases, e-mail systems, and volume managers.

The market share of the new IP SANs vendors will depend also on how much they will cover of the storage puzzle. Vendors of Fibre Channel SANs know that all too well; they've been there before.