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The Perfect SAN Array

Back when I wrote for PC Magazine, we did an issue once a year on the Perfect PC. It assembled the best features and performance parts from the various systems we'd tested over the past year, and with the help of the art department, we'd combine them into our idea of the perfect PC. Today I'd like to do the same for a SAN array, discussing the specs of the perfect midrange array.

My dream array would have no battery. Like Adaptec's server RAID cards, it would use an ultra-capacitor and flash instead. When the power fails, it dumps its write cache to MLC flash, which shouldn't take more than a minute or so.

I've always found cache battery maintenance annoying. Having to bring down a server or storage array to change the battery is like taking your car to the shop because the spare tire is flat. No fun, no progress, but reduced productivity and for most of us in the mid-market, a lost evening or weekend day. I sure hope more vendors jump on the ultracapacitor and flash bandwagon, so that in a few years we can look at cache batteries with the disdain we now have for removable disk packs.

The dream array would use SAS as the exclusive drive, and a JBOD interface. Now that Seagate and the other drive vendors are shipping both 15Krpm performance oriented and 5400-7200RPM capacity oriented drives with dual port SAS interfaces, we can standardize on SAS. As a JBOD interface, a single SAS cable carries three times the bandwidth of an 8gbps FC loop at a significantly lower cost. Even with the additional bandwidth, the SAS expander based drive chassis has to be less expensive to produce than FC SBODs, since the expander chips are off-the-shelf silicon.

The drives would include on drive disk encryption with the array controller handling all the keys so I can send failed drives back to the factory for credit without worrying about my data.

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