What's the "atomic disk write" for a Linux filesystem?

Question

From the nginx config file readme:

access_log:

An optional third parameter indicates the size of the buffer

If write buffering is used, this size cannot exceed the size of the atomic disk write for that filesystem.

Answer 1

This actually depends on the filesystem being used. This is probably referring to the stat.blksize filesystem attribute.

From the stat(2) manual page:

       struct stat {

           /* ... */

           blksize_t st_blksize;     /* blocksize for filesystem I/O */

The -f option to the stat(1) appears to display this information, and on my Linux box, it shows 4096 as the block size.