Jörg-Volker Peetz wrote: > If you are interested in retrieving some disk space on this > partition, I would suggest to reduce the percentage of diskspace > which may only be allocated by privileged processes. It is normally > 5% of the diskspace of a partition. In your case this makes ca. 1.8 > GB. To me this seems more than ever needed. If you reduce this > reserve to, e.g., 2% or ca. 700 MB, which seems to me still enough > reserve. And you gain ca. 1.1 GB free space. For the "ext" family > of file systems this can be done on the running system. > > The 5% value was introduced when storage devices were much much > smaller than today. > > What do others think about this?
There are a couple of different issues that minfree addresses. One is the simple one. Some amount should be reserved to root processes so that a non-root process can't drive the system completely out of disk space. For that the reasonable amount of disk space reserved is an absolute value that a system might need on that partitions. That part really shouldn't be a percentage of the disk but should be a finite reserved amount. The other is more subtle to understand. In the "old" days of spinning disks the allocation algorithm will try to defrag files on the fly by allocating them appropriately. That algorithm needs a certain percentage of disk space free to use scattered throughout the drive. For that algorithm it really should be a percentage. For that algorithm people would benchmark the system performance and determine a good "knee" in the performance curve at various amounts of disk fullness. The knee in the curve would usually occur somewhere around the 5% free amount. Therefore setting it to 10% would guarentee good performance. Setting it to 5% would allow more use of space on bigger disks but keep performance from getting too bad. Of course now with SSDs that standard thinking needs to be thought out again. I haven't seen any benchmark data for full SSDs. I imagine that it will have much flatter performance curves up to very full on an SSD. It would super awesome if someone has already done this performance benchmarking and would post a link to it so that we could all learn from it. So my thinking is that if it is a 3T spinning hard drive then I would still keep minfree at 5% (or 10%) for reasons of performance until and unless I see benchmark data showing otherwise. For any size of SSD I think it would be okay to reduce that to any smaller percentage that still reserved at least 500M (my best guess, may need a better guess) of disk space for the system to operate for log files and temporary files and other normal continuous activity. But remember that when the system gets very full then anything that needs just a little more disk space for a bit will fail. Not all applications deal with a full disk very well. We have been enjoying having large disks for a while and so applications rarely are tested very well for full disks. I have seen a lot of code that doesn't handle disk full properly. If it is your laptop then that isn't a big deal and you will probably know what the problem is about. But if you read your email there then it is also possible that you might lose a message or two if disk space goes to zero. Beware. If I am that close to full I will either clean or start planning the next storage upgrade to something larger. Bob The steady state of disks is full. -- Ken Thompson
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