Why Solid State Drives Won't Replace Spinning Disk -- Page 2


Flash Performance Not Always Worth the Price

Flash performance for small block I/O (less than 32 KB reads) is orders of magnitude faster than disk, but we all know that flash drives are not created equal for writes. Some are orders of magnitude faster than disk and some are maybe 10 to 20 times faster, and for that speed you pay a significant cost. The question is whether the cost justifies the expense.


Let's take a typical home PC application such as Photoshop. We all know that file sizes are growing, as cameras have ever larger sensors. A few years ago the file might have been 2 MB, but today it might be 8 MB or larger. Reading an 8 MB file on a typical SATA hard drive might take — with a seek, latency and read — 0.15 seconds, but on a flash drive maybe 0.1 seconds, depending on the drive. Does that minute difference really matter? What about editing a large video file? The disk drive might be 80 MB/sec, while the low-end flash drive might be 100 MB/sec. Again, not a huge difference. What does matter is that the metadata used for the editing application is going to go way faster on a flash drive. I know many people with more than 500 GB of data at home between music, videos and pictures. The space requirements add up very quickly. People are not going to spend even 50 percent more for small performance increases at home.

Back in the early 1990s, I had a tape backup system for my home PC. Tape for home PCs is a thing of the past, never to return, but I don't see flash hurting disk to the extent that disk has hurt tape sales. Flash technology won't achieve the densities of hard drives at anywhere near the same cost, at least anytime soon. There are just far too many challenges. Flash and hard drives will have to coexist, and if flash vendors don't see that, they will risk missing their target market, as cheap bulk storage is needed for most data just as much as small block random I/O is essential for a few use cases.

My next PC at home, for Photoshop editing, personal finances and long-term storage, will be a Windows PC with a small flash drive with a home NAS box with four 2TB hard drives connected over 10 Gb Ethernet (at least that's my hope). I will use the flash drive for booting and for temporary files for Photoshop editing, and the bulk NAS storage for pictures, videos, music and everything else.

Hybrid storage requirements are here to stay. Flash addresses the problem for small files, small application I/O requests and swapping far better than hard drives ever will. Flash will never have the price/density advantage of hard drives, however. Solid state technology will have a significant impact on hard drive companies, but flash alone will never be able to meet storage density requirements. Welcome to the new tape vs. disk argument, and expect the same results. Disk isn't going away, no matter how hard some vendors wish.


Henry Newman, CTO of Instrumental Inc. and a regular Enterprise Storage Forum contributor, is an industry consultant with 28 years experience in high-performance computing and storage.
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