On Thu, Feb 7, 2019 at 7:25 PM David T-G <davidtg@xxxxxxxxxxxxxxx> wrote: > > diskfarm:root:6:~> mdadm --detail /dev/md0 > /dev/md0: > Version : 1.2 Version 1.2 metadata is 4K offset from the start of the member device. The member devices in your case: > Number Major Minor RaidDevice State > 0 8 17 0 active sync /dev/sdb1 > 1 8 65 1 active sync /dev/sde1 > 3 8 81 2 active sync /dev/sdf1 > 4 8 1 3 active sync /dev/sda1 That means those member devices are partitioned. The primary GPT will be in the first 34 512 byte sectors, and backup GPT in the last 34 512 byte sectors, on each physical drive. The mdadm v1.2 superblock is located at 4K from the start of the partition designated as a member of the array. And mdadm will only consider the partition as the area that can be written to which means each member device's backup GPT should be immune from being written to by md and XFS. Since there's a 512KiB chunk size, and the array is clearly also partitioned, means the array primary GPT is on one member device soon after the mdadm superblock; and the array backup GPT is on a different member device immediately before its own backup GPT. I can't think of a reason for a conflict off the top of my head. And yet there's a conflict somewhere as you have independent corruptions: XFS and GPT. Just - whatever you do, don't fix anything. Here's an idea for setting up an overlay so you can test your repairs by writing changes elsewhere, and not touch the original drives. https://raid.wiki.kernel.org/index.php/Recovering_a_failed_software_RAID#Making_the_harddisks_read-only_using_an_overlay_file I suggest getting advice on the linux-raid list before proceeding, find out why it appears XFS and the array backup GPT are being stepped on. They'll want to see the partitioning for every device (both primary and backup if they aren't identical, i.e. one is corrupt), the full superblock for each device, and the GPT for the array. And what version of mdadm was used to create the array. They'll also want smartctl -x for each drive. And they'll want 'smartctl -l scterc' from each drive. And they'll want to know what the kernel command timer is set to for each drive: # cat /sys/block/sdX/device/timeout I imagine you're gonna get asked by someone why bother partitioning each drive with one partition, and then partition the array too, also with one partition. That's overly complicated and serves no purpose. Next time, make each whole drive an mdadm member; and then format the array. People lose their data all the time due to user error, so I can't recommend enough that you sanity check what you've done and what you intend to do, on each applicable list, using linux-raid for the mdadm stuff. And for godsake if you care at all about this data you need at least one backup copy. -- Chris Murphy
