md/raid1,raid10: don't broken array on failfast metadata write fails #226
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Upstream branch: c17fb54 |
A super_write IO failure with MD_FAILFAST must not cause the array to fail. Because a failfast bio may fail even when the rdev is not broken, so IO must be retried rather than failing the array when a metadata write with MD_FAILFAST fails on the last rdev. A metadata write with MD_FAILFAST is retried after failure as follows: 1. In super_written, MD_SB_NEED_REWRITE is set in sb_flags. 2. In md_super_wait, which is called by the function that executed md_super_write and waits for completion, -EAGAIN is returned because MD_SB_NEED_REWRITE is set. 3. The caller of md_super_wait (such as md_update_sb) receives a negative return value and then retries md_super_write. 4. The md_super_write function, which is called to perform the same metadata write, issues a write bio without MD_FAILFAST this time. When a write from super_written without MD_FAILFAST fails, the array may broken, and MD_BROKEN should be set. After commit 9631abd ("md: Set MD_BROKEN for RAID1 and RAID10"), calling md_error on the last rdev in RAID1/10 always sets the MD_BROKEN flag on the array. As a result, when failfast IO fails on the last rdev, the array immediately becomes failed. This commit prevents MD_BROKEN from being set when a super_write with MD_FAILFAST fails on the last rdev, ensuring that the array does not become failed due to failfast IO failures. Failfast IO failures on any rdev except the last one are not retried and are marked as Faulty immediately. This minimizes array IO latency when an rdev fails. Fixes: 9631abd ("md: Set MD_BROKEN for RAID1 and RAID10") Signed-off-by: Kenta Akagi <k@mgml.me>
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Upstream branch: c17fb54 |
Once MD_BROKEN is set on an array, no further writes can be performed to it. The user must be informed that the array cannot continue operation. Signed-off-by: Kenta Akagi <k@mgml.me>
Since commit 9a56784 ("md: allow last device to be forcibly removed from RAID1/RAID10."), RAID1/10 arrays can now lose all rdevs. Before that commit, losing the array last rdev or reaching the end of the function without early return in raid{1,10}_error never occurred. However, both situations can occur in the current implementation. As a result, when mddev->fail_last_dev is set, a spurious pr_crit message can be printed. This patch prevents "Operation continuing" printed if the array is not operational. root@fedora:~# mdadm --create --verbose /dev/md0 --level=1 \ --raid-devices=2 /dev/loop0 /dev/loop1 mdadm: Note: this array has metadata at the start and may not be suitable as a boot device. If you plan to store '/boot' on this device please ensure that your boot-loader understands md/v1.x metadata, or use --metadata=0.90 mdadm: size set to 1046528K Continue creating array? y mdadm: Defaulting to version 1.2 metadata mdadm: array /dev/md0 started. root@fedora:~# echo 1 > /sys/block/md0/md/fail_last_dev root@fedora:~# mdadm --fail /dev/md0 loop0 mdadm: set loop0 faulty in /dev/md0 root@fedora:~# mdadm --fail /dev/md0 loop1 mdadm: set device faulty failed for loop1: Device or resource busy root@fedora:~# dmesg | tail -n 4 [ 1314.359674] md/raid1:md0: Disk failure on loop0, disabling device. md/raid1:md0: Operation continuing on 1 devices. [ 1315.506633] md/raid1:md0: Disk failure on loop1, disabling device. md/raid1:md0: Operation continuing on 0 devices. root@fedora:~# Fixes: 9a56784 ("md: allow last device to be forcibly removed from RAID1/RAID10.") Signed-off-by: Kenta Akagi <k@mgml.me>
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Pull request for series with
subject: md/raid1,raid10: don't broken array on failfast metadata write fails
version: 1
url: https://patchwork.kernel.org/project/linux-raid/list/?series=990464