Give useful message if raid4/5/6 cannot be started because it is not clean and is also degraded.

Assemble.c

@@ -111,6 +111,7 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 	 *    START_ARRAY
 	 *
 	 */
+	int clean = 0;
 	int must_close = 0;
 	int old_linux = 0;
 	int vers = 0; /* Keep gcc quite - it really is initialised */
@@ -583,6 +584,7 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 	}
 
 	st->ss->getinfo_super(&info, first_super);
+	clean = info.array.state & 1;
 
 	/* now we have some devices that might be suitable.
 	 * I wonder how many
@@ -617,7 +619,7 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 		}
 	}
 	while (force && !enough(info.array.level, info.array.raid_disks,
-				info.array.layout,
+				info.array.layout, 1,
 				avail, okcnt)) {
 		/* Choose the newest best drive which is
 		 * not up-to-date, update the superblock
@@ -758,6 +760,7 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 		change += st->ss->update_super(&info, super, "force-array",
 					devices[chosen_drive].devname, verbose,
 					       0, NULL);
+		clean = 1;
 	}
 
 	if (change) {
@@ -894,7 +897,8 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 		
 		if (runstop == 1 ||
 		    (runstop <= 0 &&
-		     ( enough(info.array.level, info.array.raid_disks, info.array.layout, avail, okcnt) &&
+		     ( enough(info.array.level, info.array.raid_disks,
+			      info.array.layout, clean, avail, okcnt) &&
 		       (okcnt >= req_cnt || start_partial_ok)
 			     ))) {
 			if (ioctl(mdfd, RUN_ARRAY, NULL)==0) {
@@ -937,6 +941,19 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 			}
 			fprintf(stderr, Name ": failed to RUN_ARRAY %s: %s\n",
 				mddev, strerror(errno));
+
+			if (!enough(info.array.level, info.array.raid_disks,
+				    info.array.layout, 1, avail, okcnt))
+				fprintf(stderr, Name ": Not enough devices to "
+					"start the array.\n");
+			else if (!enough(info.array.level,
+					 info.array.raid_disks,
+					 info.array.layout, clean,
+					 avail, okcnt))
+				fprintf(stderr, Name ": Not enough devices to "
+					"start the array while not clean "
+					"- consider --force.\n");
+
 			if (must_close) close(mdfd);
 			return 1;
 		}
@@ -953,8 +970,16 @@ int Assemble(struct supertype *st, char *mddev, int mdfd,
 			fprintf(stderr, Name ": %s assembled from %d drive%s", mddev, okcnt, okcnt==1?"":"s");
 			if (sparecnt)
 				fprintf(stderr, " and %d spare%s", sparecnt, sparecnt==1?"":"s");
-			if (!enough(info.array.level, info.array.raid_disks, info.array.layout, avail, okcnt))
+			if (!enough(info.array.level, info.array.raid_disks,
+				    info.array.layout, 1, avail, okcnt))
 				fprintf(stderr, " - not enough to start the array.\n");
+			else if (!enough(info.array.level,
+					 info.array.raid_disks,
+					 info.array.layout, clean,
+					 avail, okcnt))
+				fprintf(stderr, " - not enough to start the "
+					"array while not clean - consider "
+					"--force.\n");
 			else {
 				if (req_cnt == info.array.raid_disks)
 					fprintf(stderr, " - need all %d to start it", req_cnt);

ChangeLog

@@ -10,6 +10,8 @@ Changes Prior to this release
 	can change size.
     -   Default to --auto=yes so the array devices with 'standard' names
 	get created automatically, as this is almost always what is wanted.
+    -   Give useful message if raid4/5/6 cannot be started because it is
+	not clean and is also degraded.
 
 Changes Prior to 2.5.6 release
     -   Fix bug which meant "bitmap=xxx" in mdadm.conf was not handled

mdadm.h

@@ -456,7 +456,7 @@ extern void uuid_from_super(int uuid[4], mdp_super_t *super);
 extern int same_uuid(int a[4], int b[4], int swapuuid);
 /* extern int compare_super(mdp_super_t *first, mdp_super_t *second);*/
 extern unsigned long calc_csum(void *super, int bytes);
-extern int enough(int level, int raid_disks, int layout,
+extern int enough(int level, int raid_disks, int layout, int clean,
 		   char *avail, int avail_disks);
 extern int ask(char *mesg);
 extern unsigned long long get_component_size(int fd);

super0.c

@@ -320,6 +320,7 @@ static void getinfo_super0(struct mdinfo *info, void *sbv)
 	info->array.ctime = sb->ctime;
 	info->array.utime = sb->utime;
 	info->array.chunk_size = sb->chunk_size;
+	info->array.state = sb->state;
 	info->component_size = sb->size*2;
 
 	info->disk.state = sb->this_disk.state;

super1.c

@@ -429,6 +429,7 @@ static void getinfo_super1(struct mdinfo *info, void *sbv)
 	info->array.ctime = __le64_to_cpu(sb->ctime);
 	info->array.utime = __le64_to_cpu(sb->utime);
 	info->array.chunk_size = __le32_to_cpu(sb->chunksize)*512;
+	info->array.state = (__le64_to_cpu(sb->resync_offset)+1) ? 0 : 1;
 
 	info->data_offset = __le64_to_cpu(sb->data_offset);
 	info->component_size = __le64_to_cpu(sb->size);

util.c

@@ -170,7 +170,7 @@ void remove_partitions(int fd)
 #endif
 }
 
-int enough(int level, int raid_disks, int layout,
+int enough(int level, int raid_disks, int layout, int clean,
 	   char *avail, int avail_disks)
 {
 	int copies, first;
@@ -205,9 +205,15 @@ int enough(int level, int raid_disks, int layout,
 		return avail_disks >= 1;
 	case 4:
 	case 5:
-		return avail_disks >= raid_disks-1;
+		if (clean)
+			return avail_disks >= raid_disks-1;
+		else
+			return avail_disks >= raid_disks;
 	case 6:
-		return avail_disks >= raid_disks-2;
+		if (clean)
+			return avail_disks >= raid_disks-2;
+		else
+			return avail_disks >= raid_disks;
 	default:
 		return 0;
 	}