New 15,000 rpm disk drives. Why?

Seagate and HGST have announced 600GB 15k SAS drives. Weren't SSDs supposed to kill fast hard drives? Here's why they haven't.

Five years ago pundits predicted that SSDs would kill fast hard drives. And yet, new 15k drives are being announced and shipped.


Unlike the consumer SSD, the enterprise SSD (eSSD) is very expensive. Figure $2-$3/GB vs a quarter that for consumer SSDs. 

15k SAS drives are closer in price to the consumer SSD. If you're buying hundreds of drives that adds up fast.

But why is the enterprise SSD so costly? Several reasons, perhaps not all of them good.

  • Over-provisioning. Consumer SSDs may have 7 percent more capacity than advertised to support reasonable garbage collection performance and allow for flash die failures. While there's no general spec for eSSDs, a good one will have much more capacity, say 50 percent, to ensure performance and capacity for write-intensive workloads.
  • Dual-port SAS interface. Less common and more expensive, especially in the latest 12Gb/sec flavor.
  • More robust - and expensive - architecture to guard against data-scrambling faults .
  • Better data integrity with a maximum unrecoverable read error rate of 1 per 10E16 vs 1 per 10E14 for consumer SSDs.
  • Profits. Enterprise products carry higher margins because buyers aren't as price-sensitive.

The Storage Bits take
It may be that Seagate and other disk drive vendors are also willing to cut enterprise disk margins to keep them competitive with SSDs. Nor is it clear that the added functionality of eSSDs helps arrays work better or simply helps IT sleep better.

But whatever the case, drive vendors wouldn't be announcing new 15k drives unless some customers were lined up to buy them. Those early predictions of high-end disk drive extinction were premature.

Comments welcome, as always. If your data center is still buying 15k drives, why?