Index: head/sys/conf/NOTES
===================================================================
--- head/sys/conf/NOTES
+++ head/sys/conf/NOTES
@@ -1111,6 +1111,9 @@
 # Write-protect the md root device so that it may not be mounted writeable.
 options 	MD_ROOT_READONLY
 
+# Allow to read MD image from external memory regions
+options		MD_ROOT_MEM
+
 # Disk quotas are supported when this option is enabled.
 options 	QUOTA			#enable disk quotas
 
Index: head/sys/conf/options
===================================================================
--- head/sys/conf/options
+++ head/sys/conf/options
@@ -168,6 +168,7 @@
 MD_ROOT_FSTYPE	opt_md.h
 MD_ROOT_READONLY	opt_md.h
 MD_ROOT_SIZE	opt_md.h
+MD_ROOT_MEM	opt_md.h
 MFI_DEBUG	opt_mfi.h
 MFI_DECODE_LOG	opt_mfi.h
 MPROF_BUFFERS	opt_mprof.h
Index: head/sys/dev/md/md.c
===================================================================
--- head/sys/dev/md/md.c
+++ head/sys/dev/md/md.c
@@ -180,6 +180,10 @@
  */
 u_char mfs_root[MD_ROOT_SIZE*1024] __attribute__ ((section ("oldmfs")));
 const int mfs_root_size = sizeof(mfs_root);
+#elif defined(MD_ROOT_MEM)
+/* MD region already mapped in the memory */
+u_char *mfs_root;
+int mfs_root_size;
 #else
 extern volatile u_char __weak_symbol mfs_root;
 extern volatile u_char __weak_symbol mfs_root_end;
@@ -2074,8 +2078,12 @@
 #ifdef MD_ROOT
 	if (mfs_root_size != 0) {
 		sx_xlock(&md_sx);
+#ifdef MD_ROOT_MEM
+		md_preloaded(mfs_root, mfs_root_size, NULL);
+#else
 		md_preloaded(__DEVOLATILE(u_char *, &mfs_root), mfs_root_size,
 		    NULL);
+#endif
 		sx_xunlock(&md_sx);
 	}
 #endif