Bye-bye hard drive, hello flash

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Crummy design

An optimum hybrid design is not like that. You store the OS in NVRAM (generic - pick the technology to use like flash, etc.), read-only, with flash update as an explicit task (secured by a physical switch, even); that would be how you install the OS - with the switch in write mode. The swapfile goes to capacitor or battery-backed RAM, and is flushed either periodically to disk or on power shutdown (essentially an extended, event-driven delayed write). That gets around the limited write life of certain NVRAM technologies like flash, if that's what the drive manufacturer has chosen.

The bulk of the data is handled by a conventional, cached disk design. What's missing is the ability to augment the on-disk cache with user-addable memory - just like we do now with motherboards - but in all probability, it is more effective to increase mobo DRAM than it is to use a SODIMM-like drive RAM because of market economies of scale that make mobo DRAM cheaper (and, of course, more mobo RAM diminishes the swap activity that you are trying to speed up by adding to the drive cache, so it's a harder, more expensive way to solve the response time problem).

A neater consequence, in an ideal world, would be to have a flash reader on the drive that would allow you to put your OS configuration of choice in and boot from your flash. This is trickier because of file system issues and other considerations like previous machine state (e.g., hibernate), but not too far-fetched. It would also allow you to move up in capacity as required, and even use the flash as disposable storage as the price went down. By that I mean have a little LED light up when the write life approached 90% of maximum; toss it and use a new one (you probably want a fresh image, anyway), or try different tuning configurations. Why have 5 computers when you can have one that has 5 personalities that change with the flash?

The thing to keep in mind is that the goal of hybrid design is to provide for a fast boot and high OS responsiveness by eliminating drive spinup, seek, and rotational latency delays, as well as to protect the OS from corruption by viruses, etc. - not to speed up ALL transactions. By making the on-drive NVRAM read-only, and virtualizing writes to a shadow RAM (asymmetric drive cache addressing), you achieve that.

Having said that, if you look at current reality, it would take a sizeable amount of NVRAM (flash, whatever) to handle, for example, a full install of XP. I just installed it on a laptop from scratch, and by the time I was done, over a gig was gone. That's partly hibernation file, partly temp garbage, SP2 update rollbacks, and swapfile, so an install process that takes this into account ("Are you installing on a hybrid drive?" type installation questions, with a separate "partition" concept as the destination for the OS's persistent files) would be a minimum. I think it would open up an interesting avenue for tuners and optimizers, as well as heuristic load balancers. But that amount of flash isn't cheap; even a 512 MB flash costs as much (at present, which is the market, rather than technical, issue) as a much larger hard drive. There'd have to be a VERY significant speed increase (try the math) to warrant the extra cost. Would you prefer a fast, hybrid 100 GB drive for $100, or a slower, conventional 300 GB?

Posted by: gsteele531@...   Posted on: 01/05/06 You are currently: a Guest | Members login | Terms of Use

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