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Solid State Drives

The solid state drive (SSD) is all the rage. It is an outgrowth of the USB thumb drive that is bigger, has a direct access storage device access (rather than serial as with USB) but is still composed of electronic memory that can hold its state when the power is turned off.

The expectation is that the SSD would be very fast because there are no moving parts and it is all electronic. Anand Lal Shimpi finds that the technology isn’t all together yet in his analysis of the current state of SSD in his report The SSD Anthology: Understanding SSDs and New Drives from OCZ.

The problem has to do with how the memory is addressed and what needs to be done to re-use it. An SSD, like a hard drive, deals with storage in chunks. Unlike a hard drive, the SSD can’t just write over existing data with new data. It has to ‘erase’ the area first. The SSD also needs to abstract the actual location from its address in order to even out memory cell exercise for best life. What all this boils down to is that an attempt to write to the SSD can hiccup if the drive is running out of untrod space to put things. That can create a latency problem and that is what Anand was able to measure and compare in his tests of SSD’s.

This problem is aggravated because it is the OS that knows when a file has been deleted and not the media. That means the media cannot anticipate re-use of vacated addresses and can only prepare areas for new data when it gets a request from the OS. If it can’t temporarily cache the OS write request, it will hold up the show for a bit while it gets the prep done. That may result in delays that can add up and make the user wonder what is going on.

What Anand shows in his measurements is that the SSD can indeed enhance the user experience. A boot process can often be shortened by an order of magnitude as the system reads all of the code from storage needed to run all of its processes and startup programs. He also shows how manufacturers are struggling to understand the technology and its use properly as well. His encounter with OCZ is an example of an SSD manufacturer that took heed of Anand’s findings and took steps to improve their product.

It may yet take a while for the SSD technology to get off the leading edge: to get the capabilities tailored to needs and the costs down to mass market levels. The promise is exciting.

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