Block I/O commit level

This table illustrates how the commit= affects the time it takes to create and delete a file on an x86 PIII-450 machine with a UDMA-2 EIDE disk, running a QNX 4 filesystem.

The table shows how many 0 KB files could be created and deleted per second:

commit level Number created Number deleted
high 866 1221
medium 1030 2703
low 1211 2710
none 1407 2718

Note that at the commit=high level, all disk writes are synchronous, so there's a noticeable cost in updating the directory entries and the POSIX mtime on the parent directory. At the commit=none level, all disk writes are time-delayed in the write-behind cache, and so multiple files can be created/deleted in the in-memory block without requiring any physical disk access at all (so, of course, any power failure here would mean that those files wouldn't exist when the system is restarted).