rgw/d4n: change cache write ::open() flags

changing the default flags to O_DSYNC
a small performance improvement is observable

Signed-off-by: Mark Kogan <[email protected]>

Author: mkogan1

src/common/options/rgw.yaml.in

@@ -3932,8 +3932,11 @@ options:
   long_desc: For example, to configure synchronized I/O, fcntl-linux.h defines (converted from octal)
     O_SYNC = 1052672
     O_DSYNC = 4096
+    O_DIRECT = 16384
+    O_SYNC | O_DIRECT = 1118208
+    O_DSYNC | O_DIRECT = 65552
     (0 for no modification of the flags)
-  default: 1052672
+  default: 4096
   services:
   - rgw
   with_legacy: true