[PATCH] md: allow dirty raid[456] arrays to be started at boot (6ff8d8ec) · Commits · EulixOS / Software / Kernel

Documentation/md.txt

+24 −0

Original line number	Diff line number	Diff line
		@@ -51,6 +51,30 @@ superblock can be autodetected and run at boot time.
		The kernel parameter "raid=partitionable" (or "raid=part") means
		that all auto-detected arrays are assembled as partitionable.

		Boot time assembly of degraded/dirty arrays
		-------------------------------------------

		If a raid5 or raid6 array is both dirty and degraded, it could have
		undetectable data corruption. This is because the fact that it is
		'dirty' means that the parity cannot be trusted, and the fact that it
		is degraded means that some datablocks are missing and cannot reliably
		be reconstructed (due to no parity).

		For this reason, md will normally refuse to start such an array. This
		requires the sysadmin to take action to explicitly start the array
		desipite possible corruption. This is normally done with
		mdadm --assemble --force ....

		This option is not really available if the array has the root
		filesystem on it. In order to support this booting from such an
		array, md supports a module parameter "start_dirty_degraded" which,
		when set to 1, bypassed the checks and will allows dirty degraded
		arrays to be started.

		So, to boot with a root filesystem of a dirty degraded raid[56], use

		md-mod.start_dirty_degraded=1


		Superblock formats
		------------------

+4 −0

Original line number	Diff line number	Diff line
		@@ -1937,6 +1937,7 @@ static void md_safemode_timeout(unsigned long data)
		md_wakeup_thread(mddev->thread);
		}

		static int start_dirty_degraded;

		static int do_md_run(mddev_t * mddev)
		{
		@@ -2048,6 +2049,7 @@ static int do_md_run(mddev_t * mddev)
		mddev->recovery = 0;
		mddev->resync_max_sectors = mddev->size << 1; /* may be over-ridden by personality */
		mddev->barriers_work = 1;
		mddev->ok_start_degraded = start_dirty_degraded;

		if (start_readonly)
		mddev->ro = 2; /* read-only, but switch on first write */
		@@ -4509,6 +4511,8 @@ static int set_ro(const char val, struct kernel_param kp)
		}

		module_param_call(start_ro, set_ro, get_ro, NULL, 0600);
		module_param(start_dirty_degraded, int, 0644);


		EXPORT_SYMBOL(register_md_personality);
		EXPORT_SYMBOL(unregister_md_personality);

+11 −4

Original line number	Diff line number	Diff line
		@@ -1904,11 +1904,18 @@ static int run(mddev_t *mddev)

		if (mddev->degraded == 1 &&
		mddev->recovery_cp != MaxSector) {
		if (mddev->ok_start_degraded)
		printk(KERN_WARNING
		"raid5: starting dirty degraded array: %s"
		"- data corruption possible.\n",
		mdname(mddev));
		else {
		printk(KERN_ERR
		"raid5: cannot start dirty degraded array for %s\n",
		mdname(mddev));
		goto abort;
		}
		}

		{
		mddev->thread = md_register_thread(raid5d, mddev, "%s_raid5");

+9 −4

Original line number	Diff line number	Diff line
		@@ -1929,13 +1929,18 @@ static int run(mddev_t *mddev)
		goto abort;
		}

		#if 0 /* FIX: For now */
		if (mddev->degraded > 0 &&
		mddev->recovery_cp != MaxSector) {
		printk(KERN_ERR "raid6: cannot start dirty degraded array for %s\n", mdname(mddev));
		if (mddev->ok_start_degraded)
		printk(KERN_WARNING "raid6: starting dirty degraded array:%s"
		"- data corruption possible.\n",
		mdname(mddev));
		else {
		printk(KERN_ERR "raid6: cannot start dirty degraded array"
		" for %s\n", mdname(mddev));
		goto abort;
		}
		#endif
		}

		{
		mddev->thread = md_register_thread(raid6d, mddev, "%s_raid6");

+1 −0

Original line number	Diff line number	Diff line
		@@ -183,6 +183,7 @@ struct mddev_s
		sector_t resync_mismatches; /* count of sectors where
		* parity/replica mismatch found
		*/
		int ok_start_degraded;
		/* recovery/resync flags
		* NEEDED: we might need to start a resync/recover
		* RUNNING: a thread is running, or about to be started