What is an atomic disk for a Linux file system?

Question

From the nginx config file readme:

access_log:

An additional third parameter indicates the size of the buffer.

If write buffering is used, this size cannot exceed the size of the atomic disk record for this file system.

Answer 1

It actually depends on the file system used. This probably refers to the stat.blksize attribute for the file system.

From stat (2) man page:

       struct stat {

           /* ... */

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

The -f option for stat (1) displays this information, and in my Linux box it displays 4096 as a block size.