Concurrent I/O allows multiple processes to read from or write to the same file without blocking other read(2) or write(2) calls. POSIX semantics requires read and write calls to be serialized on a file with other read and write calls. Concurrent I/O is generally used by applications that require high performance for accessing data and do not perform overlapping writes to the same file.

Veritas Storage Foundation supports concurrent I/O for applications running in the non-global zones as well. This implies that a process in a non-global zone can access the file concurrently with other processes in the global or non-global zone. The application or running threads are responsible for coordinating the write activities to the same file when using Concurrent I/O.

An application must perform the following activities to enable the concurrent I/O advisory on a file:

  fd=open(filename, oflag)
  ioctl(fd, VX_SETCACHE, VX_CONCURRENT)
  write(fd, buff, numofbytes)