Recovering a 4xhdd RAID10 file system with 2 failed disks Hi all, Quick and Dirty: 4disk RAID10 with 2 missing devices, mounts as degraded,ro , readonly scrub ends with no errors Recovery options: A/ If you had at least 3 hdds, you could replace/add a device B/ If you only have 2 hdds, even if scrub ro is ok, you cannot replace/add a device So I guess the best option is: B.1/ create a new RAID0 filesystem , copy data over to the new filesystem, add the old drives to the new filesystem, re-balance the system as RAID10. B.2/ any other ways to recover that I am missing ? anything easier/faster ? Long story: A couple of weeks back I had a failed hdd in a RAID10 4disk btrfs. I added a new device, removed the failed, but three days later after the recovery, I ended up with another 2 failing disks. So I physically removed the failing 2 disks from the drive bays. (sent one back to Seagate for replacement, the other one I kept it and will send it later) (please note I do have a backup) Good thing is that the two drives I have left in this RAID10 , seem to hold all data and data seems ok according to a read-only scrub. The remaining 2 disks from the RAID can be mounted with –o degraded,ro I did a read-only scrub on the filesystem (while mounted as –o degraded,ro) and scrub ended with no errors. I hope this ro scrub is 100% validation that I have not lost any files, and all files are ok. Just today I *tried* to inserted a new disk, and add it to the RAID10 setup. If I mount the filesystem as degraded,ro I cannot add a new device (btrfs device add). And I cannot replace a disk (btrfs replace –r start). That is because the filesystem is mounted not only as degraded but as read-only. But a two disk RAID10, can only be mounted as ro. This is by design gitorious.org/linux-n900/linux-n900/commit /bbb651e469d99f0088e286fdeb54acca7bb4ad4e But again, a RAID10 system should be recoverable somehow if the data is all there but half of the disks are missing. ( Ie. the raid0 drives are there and only the raid1 part is missing. The striped volume is ok, the mirror data is missing) If it was an ordinary RAID10 , replacing the two mirror disks at the same time should be acceptable and the RAID should be recoverable. Myself I am lucky , since I still have one of the old failing disks in my hands. (the other one is being RMAd currently) I can insert the old failing disk and mount the file system as degraded (but not ro), and then run a btrfs replace or btrfs device add. But in case I did not have the old failing disk in my hands, or if the disk was damaged beyond recognition/repair (eg not recognized in BIOS), as far as I understand it is impossible to add/replace drives in a file system mounted as read-only. Am I missing something ? Is there a better and faster way to recover a RAID10 when only the striped data is there but not the mirror data? Thanks in advance, TM -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html