diff --git a/Assemble.c b/Assemble.c
index c0ed917..d765001 100644
--- a/Assemble.c
+++ b/Assemble.c
@@ -719,6 +719,7 @@ int Assemble(struct supertype *st, char *mddev,
 		/* This is a member of a container.  Try starting the array. */
 		int err;
 		err = assemble_container_content(st, mdfd, content, runstop,
+						 readonly,
 						 chosen_name, verbose,
 						 backup_file, freeze_reshape);
 		close(mdfd);
@@ -1378,6 +1379,11 @@ int Assemble(struct supertype *st, char *mddev,
 					rv = Grow_continue(mdfd, st, content,
 							   backup_file,
 							   freeze_reshape);
+			} else if (readonly &&
+				   sysfs_attribute_available(
+					   content, NULL, "array_state")) {
+				rv = sysfs_set_str(content, NULL,
+						   "array_state", "readonly");
 			} else
 #endif
 				rv = ioctl(mdfd, RUN_ARRAY, NULL);
@@ -1543,6 +1549,7 @@ int Assemble(struct supertype *st, char *mddev,
 #ifndef MDASSEMBLE
 int assemble_container_content(struct supertype *st, int mdfd,
 			       struct mdinfo *content, int runstop,
+			       int readonly,
 			       char *chosen_name, int verbose,
 			       char *backup_file, int freeze_reshape)
 {
@@ -1556,12 +1563,18 @@ int assemble_container_content(struct supertype *st, int mdfd,
 	sysfs_init(content, mdfd, 0);
 
 	sra = sysfs_read(mdfd, 0, GET_VERSION);
-	if (sra == NULL || strcmp(sra->text_version, content->text_version) != 0)
+	if (sra == NULL || strcmp(sra->text_version, content->text_version) != 0) {
+		if (content->array.major_version == -1 &&
+		    content->array.minor_version == -2 &&
+		    readonly &&
+		    content->text_version[0] == '/')
+			content->text_version[0] = '-';
 		if (sysfs_set_array(content, md_get_version(mdfd)) != 0) {
 			if (sra)
 				sysfs_free(sra);
 			return 1;
 		}
+	}
 
 	/* There are two types of reshape: container wide or sub-array specific
 	 * Check if metadata requests blocking container wide reshapes
@@ -1628,7 +1641,7 @@ int assemble_container_content(struct supertype *st, int mdfd,
 		case LEVEL_MULTIPATH:
 		case 0:
 			err = sysfs_set_str(content, NULL, "array_state",
-					    "active");
+					    readonly ? "readonly" : "active");
 			break;
 		default:
 			err = sysfs_set_str(content, NULL, "array_state",
diff --git a/Incremental.c b/Incremental.c
index 44d5c7c..009d88c 100644
--- a/Incremental.c
+++ b/Incremental.c
@@ -44,7 +44,8 @@ static int try_spare(char *devname, int *dfdp, struct dev_policy *pol,
 
 static int Incremental_container(struct supertype *st, char *devname,
 				 char *homehost,
-				 int verbose, int runstop, int autof,
+				 int verbose, int runstop,
+				 int readonly, int autof,
 				 int freeze_reshape);
 
 int Incremental(char *devname, int verbose, int runstop,
@@ -139,7 +140,8 @@ int Incremental(char *devname, int verbose, int runstop,
 				pr_err("failed to get "
 				       "exclusive lock on mapfile\n");
 			rv = Incremental_container(st, devname, homehost,
-						   verbose, runstop, autof,
+						   verbose, runstop,
+						   0, autof,
 						   freeze_reshape);
 			map_unlock(&map);
 			return rv;
@@ -451,7 +453,7 @@ int Incremental(char *devname, int verbose, int runstop,
 		sysfs_free(sra);
 		if (!rv)
 			rv = Incremental_container(st, chosen_name, homehost,
-						   verbose, runstop, autof,
+						   verbose, runstop, 0, autof,
 						   freeze_reshape);
 		map_unlock(&map);
 		if (rv == 1)
@@ -1335,7 +1337,8 @@ static char *container2devname(char *devname)
 
 static int Incremental_container(struct supertype *st, char *devname,
 				 char *homehost, int verbose,
-				 int runstop, int autof, int freeze_reshape)
+				 int runstop, int readonly,
+				 int autof, int freeze_reshape)
 {
 	/* Collect the contents of this container and for each
 	 * array, choose a device name and assemble the array.
@@ -1470,7 +1473,7 @@ static int Incremental_container(struct supertype *st, char *devname,
 			return 2;
 		}
 
-		assemble_container_content(st, mdfd, ra, runstop,
+		assemble_container_content(st, mdfd, ra, runstop, readonly,
 					   chosen_name, verbose, NULL,
 					   freeze_reshape);
 		close(mdfd);
diff --git a/ReadMe.c b/ReadMe.c
index b6aac0b..35ffeaa 100644
--- a/ReadMe.c
+++ b/ReadMe.c
@@ -440,6 +440,7 @@ char Help_assemble[] =
 "                     : out-of-date.  This involves modifying the superblocks.\n"
 "  --update=     -U   : Update superblock: try '-A --update=?' for option list.\n"
 "  --no-degraded      : Assemble but do not start degraded arrays.\n"
+"  --readonly    -o   : Mark the array as read-only. No resync will start.\n"
 ;
 
 char Help_manage[] =
diff --git a/mdadm.8.in b/mdadm.8.in
index 1a7cba7..33919bd 100644
--- a/mdadm.8.in
+++ b/mdadm.8.in
@@ -831,6 +831,13 @@ initial resync work faster).  With
 .I mdadm
 will not try to be so clever.
 
+.TP
+.BR \-o ", " \-\-readonly
+Start the array
+.B read only
+rather than read-write as normal.  No writes will be allowed to the
+array, and no resync, recovery, or reshape will be started.
+
 .TP
 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
 Instruct mdadm how to create the device file if needed, possibly allocating
diff --git a/mdadm.c b/mdadm.c
index d346240..e10fc38 100644
--- a/mdadm.c
+++ b/mdadm.c
@@ -707,6 +707,12 @@ int main(int argc, char *argv[])
 			}
 			continue;
 
+		case O(ASSEMBLE,'o'):
+		case O(MANAGE,'o'):
+		case O(CREATE,'o'):
+			readonly = 1;
+			continue;
+
 		case O(ASSEMBLE,'U'): /* update the superblock */
 		case O(MISC,'U'):
 			if (update) {
diff --git a/mdadm.h b/mdadm.h
index 3071c45..f96ac7b 100644
--- a/mdadm.h
+++ b/mdadm.h
@@ -1193,6 +1193,7 @@ extern int flush_metadata_updates(struct supertype *st);
 extern void append_metadata_update(struct supertype *st, void *buf, int len);
 extern int assemble_container_content(struct supertype *st, int mdfd,
 				      struct mdinfo *content, int runstop,
+				      int readonly,
 				      char *chosen_name, int verbose,
 				      char *backup_file, int freeze_reshape);
 extern struct mdinfo *container_choose_spares(struct supertype *st,