What HDS Math is EMC using for its 1TB drives?
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While EMC bloggers garnered media attention last year pointing out the faulty mathematics from HDS, an astute reader pointed me to EMC's own [DMX-4 specification sheet],updated for its 1TB SATA disk.I've chosen just the minimum and maximum number of drives RAID-6 data points for non-mainframe platforms:
Where EMC appears miscalculating is having 20x more drives, as the numbers don't match up. For 1920 drives inRAID-6, you would expect 20x more usable capacity than the 96 drive configurations. For 6+2 configurations, one would expect 720TB and 1440TB respectively. For 14+2 configurations, one wouldexpect 840TB and 1680TB, respectively.
Perhaps EMC DMX-4 can't address more than 600TB for the entire system? Does EMC purposely limit the benefitsof these larger drives? It does question why someone might go from 500GB to 1TB drives, if the maximum configuration only gives about 40TB more capacity.Fellow IBM blogger Barry Whyte questioned the use of SATA in an expensive DMX-4 system, in his post[One Box Fits All - Or Does It], and now perhaps there are good reasons to question 1TB from a capacityperspective as well.