Earlier this month, distributor Bell Micro sponsored a cross-country set of seminars on solid-state disks (SSDs) featuring storage expert Jim Handy as keynoter. Handy’s talk was so content rich that it’ll take several blog entries to deliver all of the delicious slices of insight from his presentation.

One of the interesting facets Handy discussed was the current practice of short-stroking enterprise-class hard disk drives (HDDs)—“abusing” them, as Handy explained. The idea’s pretty simple. An HDD’s average access time is determined by the average amount of time it takes to swing the arm carrying the read/write heads into position plus the average rotational latency. The fastest enterprise-class HDDs now spin at 15,000 RPM so there’s not much room for trimming there—not without having the disk platters fly apart under the centripetal force. However, there’s something that can be done about the average seek time. Simply use fewer of the available tracks on the disk. Doing so, you get faster average seek times because the arm never needs to travel very far.

You pay for that decreased seek time with lost capacity. You simply don’t use most of the tracks and therefore you discard most of an HDD’s storage capacity.

Handy gave the following real-world example of such HDD abuse. He described IBM’s DS8300 Turbo. It has best-in-class TPC-C specs: 123K IOPS, 16-msec latency. It gangs 512 HDDs—consisting of 73- and 146-Gbyte enterprise-class drives—into mirrored RAID arrays. The result is a storage subsystem with 53 Tbytes of actual capacity, but short-stroking the drives reduces the usable capacity to 9 Tbytes. IBM threw away 83% of the raw capacity to get those best-in-class TPC-C performance specs.

This is yet another example of why SSD manufacturers are crowding into the Flash Zone. If IBM can afford to throw away 83% of the available capacity in a huge multi-multi-Tbyte bank of enterprise-class HDDs, then high-performance SSDs that can muster one or two orders of magnitude performance improvement relative to the “rotating rust” HDDs must be worth a lot of money to data-center architects.

And apparently, they are.