SSDs vs. HDDs: Pre-game warm-up

Posted on September 01, 2008

The upcoming battle between solid-state disk (SSD) drives and traditional hard disk drives (HDDs) is looming, and the heat in the controversy is reminiscent of the old iSCSI vs. Fibre Channel debates, even though the game hasn’t really begun.

SSDs have been around for decades, but until recently they have been outrageously expensive. Prices are coming down, but from a cost-per-gigabyte perspective they’re still outrageously expensive. However, if you do the numbers on a cost-per-IOPS basis, SSDs are a fantastic deal—provided you have the need for speed.

The cost debate was fueled earlier this year when Joe Tucci, EMC's chief executive officer, predicted that SSD drive pricing will be on parity with high-end Fibre Channel drives within two to three years—a tad optimistic, perhaps, but who am I to argue with him?

The advantages of SSDs are well-known: They’re blazingly fast, at least on read operations (30 times faster than high-end Fibre Channel drives, according to EMC officials), and they consume a lot less energy (hardly a reason to buy them, but an advantage nonetheless).

Ray Lucchesi Silverton Consulting
However, the potential drawbacks are less known. In addition to high cost, SSDs can suffer from “wear out.” SSDs based on NAND technology can only handle so many writes before they fail, a condition sometimes referred to as the NAND write-endurance problem, as noted in the second article in our Special Report in this issue, “SSD flash drives enter the enterprise,” by Silverton Consulting’s Ray Lucchesi (see p. 24) .

In preparing their drives for use in enterprise-class disk arrays, SSD manufacturers mitigate this problem with technologies such as wear leveling and over-provisioning, but it’s nevertheless a potential problem if you’re considering SSDs for enterprise applications (as opposed to using them in portable systems or consumer devices).

Ray’s article provides an in-depth, realistic look at both the advantages and disadvantages of SSDs that circumvents the vendor hype surrounding the SSD vs. HDD debate.

In our next issue, we’ll cover the SSD market in detail, relying on data from the Objective Analysis semiconductor research and consulting firm.

Despite the controversy surrounding the reliability issue, and debates over the actual performance differences between SSDs and HDDs, solid-state devices will eventually play a key role in enterprise storage systems—whether they replace or just augment HDDs. This trend will be fueled by the leading disk array vendors—obviously, EMC, but other vendors such as Hitachi Data Systems, Sun and, more recently, IBM have also announced plans for SSDs. And last month, Intel introduced much-anticipated SSDs for both portables and enterprise-class arrays (see “Intel debuts SSD drives at IDF” at www.infostor.com).

Dave Simpson