Comment 6 for bug 1340448

I just don't think an adaptive algorithm is going to be worth the complexity. It will invariably get it wrong for some work load or another. At which point more people will start kvetching and opening bug reports.

For one thing, it matters a lot what the average size is of the files being stored on a file system. For example, if the average file size is 4k, then you can fill it to 100% without suffering any performance degradation. It will also depend on the distibution of the files and whether you just write once and be done, or whether files are constantly being deleted and inserted, potentially with different sizes.

It also matters whether the user cares about performance or capacity. Disks have essentially not changed the average seek time, while doubling in capacity every 18 months or so (with this trend only only slowing down in the past year or two). So if you consider the average seek per GB of capacity, it's been dropping with every single disk generation. As a result, there are probably many applications which are now no longer constrained by disk capacity, but by seek capacity (i.e., by the number of spindles). I've even seen examples of shops that have deliberately not gotten the latest 6TB or 8TB disks, because they are spindle constrained, and so they are better off buying 2T or 4T disks.

This last is why I really don't think it's worth while to worry about that last 51GB if you have a 1T disk. Adding complexity to the calculation just makes it harder for system administrators to understand what is going on, and with the seeks per GB dropping like a stone over the past few decades, for many shops performance is far more important than the value of that 51GB (which in dollar values, given today's costs in disk, is approximately $2.50 USD. In terms of minutes of a system administrators time, or a software engineers time, you've no doubt wasted far more than that in discussing it. :-)