The Importance of Free Space
MFT's real key is the use and management of free space to accelerate performance dramatically. Here, one must begin with the notion that while MFT is a block device, capable of accepting any file system, it is similar in concept to Log File Systems which also write linearly. The efficiencies of such design approaches are directly proportional to the amount of free space on these storage systems. For instance, if all space on the device is free, then the device runs at 100% efficiency, but if only 10% is free, then the efficiency is just 10%, and effective efficiency can decline below that level.
But space does not have to be physically set aside to be usable "free space." Instead, it can be virtual space or compressed space. Thus, data not actually delegated to holding files can be counted as free space, and improve efficiency. Every system has a certain amount of practically free space. Most Windows and Linux system start to get flaky when space unassigned to files falls below 10%. Similarly, systems are often over-engineered with extra free space because premature change is costly. Finally, over the life cycle of machines, systems start with extra free space, and over time have less.
Effectiveness of free space also amplifies as a statistical function of cleanup routine efficiency, and naturally occurring statistical conditions both of distribution and of repetition of things such as Inodes. These are of little value when free space only comprises five to ten percent of the drive. But they become significant when the system has a greater percentage of naturally occurring free space such as 20% or 30%. These often have the result of squaring the performance value of the free space.
All that has been described so far effects the wear life of the drive. There is one remaining issue which is free-time in the Flash Drive system. When there is free-time the system takes partially empty blocks and builds totally full as well as totally empty erase/write blocks from these. Totally empty write blocks mean that when actual writing is to be done, it will occur at the linear speed of the drive, rather than a fraction of these.
While the speed perspective is easy to understand, the second of product life enhancement is more difficult because it determines the useful life of the flash drive. That is discussed in the next section.