On Mon, Jan 09 2017, Eyal Lebedinsky wrote:

I am aware of that discussion and agree with the sentiment (fix in user space).

(I primarily provided for the information of others)

What I miss is a message from md when a 'check' mismatch is found. Not having
this means I have to run 'raid6check', then after looking at the situation
run 'raid6check autorepair' in the small sections reported as bad. This is time
consuming and risky.

Something like this?

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 69b0a169e43d..f19c38baf2b2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c

@@ -2738,6 +2738,8 @@ static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
 			conf->mddev->resync_mismatches += STRIPE_SECTORS;
 			if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
 				/* don't try to repair!! */
+				pr_debug("%s: \"check\" found inconsistency near sector %llu\n",
+					 md_name(conf->mddev), sh->sector);
 				set_bit(STRIPE_INSYNC, &sh->state);
 			else {
 				sh->check_state = check_state_compute_run;

I chose pr_debug() because I didn't want to flood the logs if there are
lots of inconsistencies.
You can selectively enable pr_debug() messages by writing to
/sys/kernel/debug/dynamic_debug/control
providing you have dynamic debugging compiled in.

Maybe use pr_info_ratelimited() instead??

NeilBrown