Index: sbin/newfs_msdos/mkfs_msdos.c
===================================================================
--- sbin/newfs_msdos/mkfs_msdos.c
+++ sbin/newfs_msdos/mkfs_msdos.c
@@ -243,8 +243,9 @@
     struct bsx *bsx;
     struct de *de;
     u_int8_t *img;
+    u_int8_t *physbuf, *physbuf_end;
     const char *bname;
-    ssize_t n;
+    ssize_t n, tailsize;
     time_t now;
     u_int fat, bss, rds, cls, dir, lsn, x, x1, x2;
     u_int extra_res, alignment, saved_x, attempts=0;
@@ -252,7 +253,7 @@
     int fd, fd1, rv;
     struct msdos_options o = *op;
 
-    img = NULL;
+    physbuf = NULL;
     rv = -1;
     fd = fd1 = -1;
 
@@ -622,10 +623,14 @@
 	}
 
 
-	if (!(img = malloc(bpb.bpbBytesPerSec))) {
+	physbuf = malloc(MAXPHYS);
+	if (physbuf == NULL) {
 	    warn(NULL);
 	    goto done;
 	}
+	physbuf_end = physbuf + MAXPHYS;
+	img = physbuf;
+
 	dir = bpb.bpbResSectors + (bpb.bpbFATsecs ? bpb.bpbFATsecs :
 				   bpb.bpbBigFATsecs) * bpb.bpbFATs;
 	memset(&si_sa, 0, sizeof(si_sa));
@@ -750,19 +755,28 @@
 		    (u_int)tm->tm_mday;
 		mk2(de->deMDate, x);
 	    }
-	    if ((n = write(fd, img, bpb.bpbBytesPerSec)) == -1) {
-		warn("%s", fname);
-		goto done;
-	    }
-	    if ((unsigned)n != bpb.bpbBytesPerSec) {
-		warnx("%s: can't write sector %u", fname, lsn);
-		goto done;
+	    img += bpb.bpbBytesPerSec;
+	    if (img >= physbuf_end) {
+		n = write(fd, physbuf, MAXPHYS);
+		if (n != MAXPHYS) {
+		    warnx("%s: can't write sector %u", fname, lsn);
+		    goto done;
+		}
+		img = physbuf;
 	    }
 	}
+	if (img != physbuf) {
+		tailsize = img - physbuf;
+		n = write(fd, physbuf, tailsize);
+		if (n != tailsize) {
+		    warnx("%s: can't write sector %u", fname, lsn);
+		    goto done;
+		}
+	}
     }
     rv = 0;
 done:
-    free(img);
+    free(physbuf);
     if (fd != -1)
 	    close(fd);
     if (fd1 != -1)