From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: [PATCH 003 of 3] md: Do not compute parity unless it is on a failed drive Date: Tue, 27 May 2008 16:32:17 +1000 Message-ID: <1080527063217.16444@suse.de> References: <20080527162558.16305.patches@notabene> Return-path: Sender: linux-raid-owner@vger.kernel.org To: Andrew Morton Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Williams , stable@kernel.org List-Id: linux-raid.ids From: Dan Williams If a block is computed (rather than read) then a check/repair operation may be lead to believe that the data on disk is correct, when infact it isn't. So only compute blocks for failed devices. This issue has been around since at least 2.6.12, but has become harder to hit in recent kernels since most reads bypass the cache. echo repair > /sys/block/mdN/md/sync_action will set the parity blocks to the correct state. Cc: Signed-off-by: Dan Williams Signed-off-by: Neil Brown ### Diffstat output ./drivers/md/raid5.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff .prev/drivers/md/raid5.c ./drivers/md/raid5.c --- .prev/drivers/md/raid5.c 2008-05-27 16:24:18.000000000 +1000 +++ ./drivers/md/raid5.c 2008-05-27 16:24:41.000000000 +1000 @@ -2002,6 +2002,7 @@ static int __handle_issuing_new_read_req * have quiesced. */ if ((s->uptodate == disks - 1) && + (s->failed && disk_idx == s->failed_num) && !test_bit(STRIPE_OP_CHECK, &sh->ops.pending)) { set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending); set_bit(R5_Wantcompute, &dev->flags); @@ -2087,7 +2088,9 @@ static void handle_issuing_new_read_requ /* we would like to get this block, possibly * by computing it, but we might not be able to */ - if (s->uptodate == disks-1) { + if ((s->uptodate == disks - 1) && + (s->failed && (i == r6s->failed_num[0] || + i == r6s->failed_num[1]))) { pr_debug("Computing stripe %llu block %d\n", (unsigned long long)sh->sector, i); compute_block_1(sh, i, 0);