Question

In HDF5 library “virtual file layer”, we can choose between several options. The default one if SEC2, which is a POSIX driver “with no system buffering”- You can also choose DIRECT, which is a variant of POSIX “except that files are written without being cached by the system”.

So, what is the difference between a file buffer and a file cache? For me it sounds pretty much like the same thing.

Answer 1

Judging from experience with other libraries having similar descriptions in their docs… these always meant:

• “with no system buffering” = “direct read” (no buffering on reads)
• “written without being cached by the system” = “direct write” (usually achieved by calling flush or similar after every write)

The second option bing slower on writing than the first one… read-speed is the same…