Commit 48cf06bc authored by Heinz Mauelshagen's avatar Heinz Mauelshagen Committed by Mike Snitzer
Browse files

dm raid: add discard support for RAID levels 4, 5 and 6 



In case of RAID levels 4, 5 and 6 we have to verify each RAID members'
ability to zero data on discards to avoid stripe data corruption -- if
discard_zeroes_data is not set for each RAID member discard support must
be disabled.  But given the uncertainty of whether or not a RAID member
properly supports zeroing data on discard we require the user to
explicitly allow discard support on RAID levels 4, 5, and 6 by setting
a dm-raid module paramter, e.g.: dm-raid.devices_handle_discard_safely=Y
Otherwise, discards could cause data corruption on RAID4/5/6.

Signed-off-by: default avatarHeinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 75b8e04b

drivers/md/dm-raid.c

+34 −4
Original line number Diff line number Diff line
@@ -18,6 +18,8 @@ 


#define DM_MSG_PREFIX "raid"



static bool devices_handle_discard_safely = false;



/*

 * The following flags are used by dm-raid.c to set up the array state.

 * They must be cleared before md_run is called.
@@ -475,6 +477,8 @@ too_many: 
 *                                      will form the "stripe"

 *    [[no]sync]			Force or prevent recovery of the

 *                                      entire array

 *    [devices_handle_discard_safely]	Allow discards on RAID4/5/6; useful if RAID

 *					member device(s) properly support TRIM/UNMAP

 *    [rebuild <idx>]			Rebuild the drive indicated by the index

 *    [daemon_sleep <ms>]		Time between bitmap daemon work to

 *                                      clear bits
@@ -1150,23 +1154,45 @@ static int analyse_superblocks(struct dm_target *ti, struct raid_set *rs) 
}



/*

 * Enable/disable discard support on RAID set depending on RAID level.

 * Enable/disable discard support on RAID set depending on

 * RAID level and discard properties of underlying RAID members.

 */

static void configure_discard_support(struct dm_target *ti, struct raid_set *rs)

{

	int i;

	bool raid456;



	/* Assume discards not supported until after checks below. */

	ti->discards_supported = false;



	/* RAID level 4,5,6 require discard_zeroes_data for data integrity! */

	if (rs->md.level == 4 || rs->md.level == 5 || rs->md.level == 6)

		return; /* discard_zeroes_data cannot be trusted as reliable */

	raid456 = (rs->md.level == 4 || rs->md.level == 5 || rs->md.level == 6);



	for (i = 0; i < rs->md.raid_disks; i++) {

		struct request_queue *q = bdev_get_queue(rs->dev[i].rdev.bdev);



		if (!q || !blk_queue_discard(q))

			return;



		if (raid456) {

			if (!q->limits.discard_zeroes_data)

				return;

			if (!devices_handle_discard_safely) {

				DMERR("raid456 discard support disabled due to discard_zeroes_data uncertainty.");

				DMERR("Set dm-raid.devices_handle_discard_safely=Y to override.");

				return;

			}

		}

	}



	/* All RAID members properly support discards */

	ti->discards_supported = true;



	/*

	 * RAID1 and RAID10 personalities require bio splitting,

	 * RAID0/4/5/6 don't and process large discard bios properly.

	 */

	ti->split_discard_bios = true;

	ti->split_discard_bios = !!(rs->md.level == 1 || rs->md.level == 10);

	ti->num_discard_bios = 1;

}
@@ -1709,6 +1735,10 @@ static void __exit dm_raid_exit(void) 
module_init(dm_raid_init);

module_exit(dm_raid_exit);



module_param(devices_handle_discard_safely, bool, 0644);

MODULE_PARM_DESC(devices_handle_discard_safely,

		 "Set to Y if all devices in each array reliably return zeroes on reads from discarded regions");



MODULE_DESCRIPTION(DM_NAME " raid4/5/6 target");

MODULE_ALIAS("dm-raid1");

MODULE_ALIAS("dm-raid10");

CRA Git | Maintained and supported by SUSTech CRA and CCSE