In this new world, magnetic disks provide high-capacity, inexpensive storage and
bandwidth—cold storage and archive. Flash disks provide nonvolatile storage for hot
and warm data. Flash may also be used within disk drives to buffer writes and to provide
safe write caching. In this new world, disks look much more like tapes, and flash disks
fill the direct-access block storage role traditionally filled by magnetic disks. Flash is a
better disk (more IOPS, 10 times less latency), however, and disk is a better tape (no
rewind, mount times measured in milliseconds). Flash cost per gigabyte is far below the
disk prices of five years ago, and disk cost per gigabyte is far better than tape when one
considers the total system cost (readers, software, and operations). Thus, these changes
are very welcome. Q
1. Hwang, C. 2003. Nanotechnology enables a new memory growth model.
Proceedings of the IEEE 91( 11): 1765-1771; http://ieeexplore.ieee.org/Xplore/login.jsp?url=/
2. This Web site ( http://www.dvnation.com/nand-flash-ssd.html) had a PQI flash disk
for $1,800. The marginal cost is about $20 per gigabyte for flash today, so this device
might be had for about $600, comparable to the price of a 15,000-RPM SCSI disk.
3. Zushman, J. 2006. Hard drives go flash: Samsung Flash SSD. Tom’s Hardware; http://
4. Nath, S., Kansal, A. Flash DB: Dynamic self-tuning database for NAND flash. Microsoft
Research Technical Report MSR-TR-2006-168; ftp://ftp.research.microsoft.com/pub/tr/
5. Birrell, A., Isard, M., Thacker, C., Wobber, T. 2005. A design for high-performance
flash disks. Microsoft Research Technical Report MSR-TR-2005-176; ftp://ftp.research.
6. See reference 5.
7. See reference 5.
This article was prepared with help from Aaron Dietrich, Dennis Fetterly, James
Hamilton, and Chuck Thacker.
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