1) If nrpos <= 1, don't output rpos table (and set fs_cpc to 0) - disabling

   the use of the rotational position table.
2) Allow specification of 0 rotational positions (disables function).
3) Make rotdelay=0 and nrpos=0 by default.

   The purpose of the above is to optimize for modern SCSI (and IDE) drives
that do read-ahead/write-behind.

2 files changed, 23 insertions, 13 deletions

diff --git a/sbin/newfs/mkfs.c b/sbin/newfs/mkfs.c
index 398f369..9d71c20 100644
--- a/sbin/newfs/mkfs.c
+++ b/sbin/newfs/mkfs.c
@@ -443,7 +443,7 @@ mkfs(pp, fsys, fi, fo)
 	sblock.fs_npsect = nphyssectors;
 	sblock.fs_postblformat = FS_DYNAMICPOSTBLFMT;
 	sblock.fs_sbsize = fragroundup(&sblock, sizeof(struct fs));
-	if (sblock.fs_ntrak == 1) {
+	if (sblock.fs_ntrak == 1 || sblock.fs_nrpos <= 1) {
 		sblock.fs_cpc = 0;
 		goto next;
 	}
diff --git a/sbin/newfs/newfs.c b/sbin/newfs/newfs.c
index c7748e8..62fde30 100644
--- a/sbin/newfs/newfs.c
+++ b/sbin/newfs/newfs.c
@@ -104,12 +104,17 @@ void	fatal();
 #define	DESCPG		16	/* desired fs_cpg */
 
 /*
- * ROTDELAY gives the minimum number of milliseconds to initiate
- * another disk transfer on the same cylinder. It is used in
- * determining the rotationally optimal layout for disk blocks
- * within a file; the default of fs_rotdelay is 4ms.
+ * Once upon a time...
+ *    ROTDELAY gives the minimum number of milliseconds to initiate
+ *    another disk transfer on the same cylinder. It is used in
+ *    determining the rotationally optimal layout for disk blocks
+ *    within a file; the default of fs_rotdelay is 4ms.
+ *
+ * ...but now we make this 0 to disable the rotdelay delay because
+ * modern drives with read/write-behind achieve higher performance
+ * without the delay.
  */
-#define ROTDELAY	4
+#define ROTDELAY	0
 
 /*
  * MAXBLKPG determines the maximum number of data blocks which are
@@ -126,13 +131,18 @@ void	fatal();
 #define	NFPI		4
 
 /*
- * For each cylinder we keep track of the availability of blocks at different
- * rotational positions, so that we can lay out the data to be picked
- * up with minimum rotational latency.  NRPOS is the default number of
- * rotational positions that we distinguish.  With NRPOS of 8 the resolution
- * of our summary information is 2ms for a typical 3600 rpm drive.
+ * Once upon a time...
+ *    For each cylinder we keep track of the availability of blocks at different
+ *    rotational positions, so that we can lay out the data to be picked
+ *    up with minimum rotational latency.  NRPOS is the default number of
+ *    rotational positions that we distinguish.  With NRPOS of 8 the resolution
+ *    of our summary information is 2ms for a typical 3600 rpm drive.
+ *
+ * ...but now we make this 1 (which disables the rotational position table)
+ * because modern drives with read-ahead and write-behind do better without
+ * the rotational position table.
  */
-#define	NRPOS		8	/* number distinct rotational positions */
+#define	NRPOS		0	/* number distinct rotational positions */
 
 
 int	mfs;			/* run as the memory based filesystem */
@@ -269,7 +279,7 @@ main(argc, argv)
 				fatal("%s: bad free space %%\n", optarg);
 			break;
 		case 'n':
-			if ((nrpos = atoi(optarg)) <= 0)
+			if ((nrpos = atoi(optarg)) < 0)
 				fatal("%s: bad rotational layout count\n",
 				    optarg);
 			break;