Task #11059: O_DIRECT requires 4k alignment on Lustre

RTCP/Cobalt/OutputProc/src/FastFileStream.h

@@ -43,7 +43,9 @@ namespace LOFAR
       virtual size_t size();
 
       // formally, the required alignment for O_DIRECT is determined by the file system
-      static const size_t alignment = 512;
+      // for local disks, 512 is a typical default.
+      // for Lustre, 4096 is required.
+      static const size_t alignment = 4096;
     private:
       // writes the remainder, padded with zeros if needed. Returns the number of zero-pad bytes written.
       size_t writeRemainder();