From c21588be7046bb3d7bd091ae876732b52e04ef6e Mon Sep 17 00:00:00 2001 From: Tomasz Majchrzak Date: Fri, 12 May 2017 14:26:10 +0200 Subject: [PATCH] raid1: prefer disk without bad blocks If an array consists of two drives and the first drive has the bad block, the read request to the region overlapping the bad block chooses the same disk (with bad block) as device to read from over and over and the request gets stuck. If the first disk only partially overlaps with bad block, it becomes a candidate ("best disk") for shorter range of sectors. The second disk is capable of reading the entire requested range and it is updated accordingly, however it is not recorded as a best device for the request. In the end the request is sent to the first disk to read entire range of sectors. It fails and is re-tried in a moment but with the same outcome. Actually it is quite likely scenario but it had little exposure in my test until commit 715d40b93b10 ("md/raid1: add failfast handling for reads.") removed preference for idle disk. Such scenario had been passing as second disk was always chosen when idle. Reset a candidate ("best disk") to read from if disk can read entire range. Do it only if other disk has already been chosen as a candidate for a smaller range. The head position / disk type logic will select the best disk to read from - it is fine as disk with bad block won't be considered for it. Signed-off-by: Tomasz Majchrzak Signed-off-by: Shaohua Li --- drivers/md/raid1.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index a17ed6218d516..af5056d568788 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -666,8 +666,11 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect break; } continue; - } else + } else { + if ((sectors > best_good_sectors) && (best_disk >= 0)) + best_disk = -1; best_good_sectors = sectors; + } if (best_disk >= 0) /* At least two disks to choose from so failfast is OK */ -- 2.39.5