The Deliverator – Wannabee

So open minded, my thoughts fell out…

The Bane of the HDD?

Posted by Deliverator on August 22nd, 2005

Hard disk technology is one of the last weak links in computer performance. Despite faster spindle speeds (maxing out at 10K rpm for desktop, 15K on high end server), higher density platters (133 GB on a single platter), new bus technologies (SATA) and intelligent cache controllers (NCQs), hard disk technology still reaches transfer speeds of only 60-70MB/sec read and 25-30MB/sec write, with random access times above 5ms. That may sound pretty fast, but consider that the (volatile) DDR ram found in most desktop systems these days can transfer on the order of 1500 MB/sec with near instantaneous access times. In short, it takes a long time to move data from bulk storage to working memory, but once there, your cpu can fiddle with bits in memory at incredible speeds.

Hard disk technology is improving, but only incrementally, and at a far slower pace than other computer subsystems. Perpendicular recording technology, now shipping on some 1.8″ hard disks designed for MP3 players, shows some promise of increasing data storage densities to 2-3 times that of current. While this does mean you will be able to store more porn/volume, it is only a marginal improvement at best. Hard drives remain an unreliable mechanical disaster waiting to happen.

What is direly needed is commercial R&D and actual product development from major storage manufacturers. We continually hear about some researcher achieving 1 TB holographic storage densities on blocks of crystal the size of a quarter, but we never see any attempts to productize this research. I think there is as much reluctace to rock the boat in the storage industry as there has been in the US car (lets be frank, SUV) industry. Detroit is now paying the price for being defenders of the status que, as superior engineered cars from Asia and Europe (that get vastly better gas mileage as well) flood the US car market.

Samsung recently introduced a 16 GB solid state notebook hard disk based on NAND flash technology. Early specs claim performance similar to top of the line 7200 RPM hard drives. Considering that the technology is marketed at notebook users, where 4200 & 5200 RPM drives are the norm, this technology likely performs well above the norm. Such solid state drives have some great advantages over mechanical hard drives:

  • low power consumption means much greater battery life.
  • no moving parts means greater resistance to shock/drop damage
  • much wider operational temperature range (and lower heat production) means these drives can be used in far harsher environments than convential hard drives, and won’t fry parts of one’s anatomy that most people treasure when used in laptop systems

This technology is far from perfect. It doesn’t offer near the storage capacities of conventional hard disk technology, and likely suffers from the same limited, write wear induced life cycle to which all flash based technologies are susceptible. In brief, each flash memory “cell” can only be written to a limited number of times. While most of your data doesn’t change that often (necessitating a write), some areas of the disk are written to near constantly (paging/swap file). One approach is to use an operating system, such as Debian Linux, which can be set up to be mounted “read only” and to store logs and other, largely useless, frequently written files in ram. This technique has been used for years in the Pebble Linux Distribution, which is a specialized Linux distro for use in embedded wireless applications (which frequently boot from compact flash cards). Another approach is a technique called “wear leveling,”which attempts to stave off the inevitable by distributing writes across the disk. A final approach, which I feel holds the most promise, are hybrid disks. Such disks would combine flash based and conventional platter based technologies into a single device. Samsung is currently developing this idea along with Microsoft and it is slated to be included in Longhorn/Vista. Then again,
Microsoft has already dropped a lot of major “campaign promise” features from Longhorn, so I find it a little odd that this is where they are placing their focus.