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: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 030e2d6..4857fa4 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -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 @@
* 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 @@
}
/*
- * 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 @@
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");