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My home NAS runs btrfs in RAID 5. The key is to use software RAID / LVM to present a single block device to btrfs. That way you never use btrfs's screwed-up RA

My home NAS runs btrfs in RAID 5. The key is to use software RAID / LVM to present a single block device to btrfs. That way you never use btrfs's screwed-up RAID 5/6 implementation.

Youden 7y ago
If you use LVM/mdadm for RAID, it's not possible for btrfs to correct checksum mismatches (i.e. protect against bitrot).
- brianpgordon 7y ago
  That's a good point, though Synology (my brand of NAS) claims that they've developed analogous corruption checks operating at the LVM level, so you get the benefits of btrfs (including checksum checks and RAID scrubbing) without having to actually use its RAID implementation. https://www.synology.com/en-global/knowledgebase/DSM/help/DSM/StorageManager/storage_pool_data_scrubbing https://www.synology.com/en-global/knowledgebase/DSM/help/DS...
  - Youden 7y ago
    I wasn't actually able to find any real documentation on how Synology's SHR works. Their recovery documentation [0] indicates that SHR is just plain mdadm + LVM and a couple of NAS recovery sites [1,2] indicate the same. In the end I got a Reddit post [3] with a response from a Synology representative who says that the btrfs filesystem will request a read from a redundant copy from mdadm in order to correct checksum errors. I wonder whether this is unique to Synology or whether the change has been upstreamed into the main Linux kernel. [0]: https://www.synology.com/en-global/knowledgebase/DSM/tutorial/Storage/How_can_I_recover_data_from_my_DiskStation_using_a_PC https://www.synology.com/en-global/knowledgebase/DSM/tutoria... [1]: https://support.reclaime.com/kb/article/8-synology-shr-raid/ https://support.reclaime.com/kb/article/8-synology-shr-raid/ [2]: http://www.nas-recovery.com/kb_hybrydraid.php http://www.nas-recovery.com/kb_hybrydraid.php [3]: https://www.reddit.com/r/DataHoarder/comments/5yb13m/anyone_using_synologys_dsm_61_able_to_confirm/ https://www.reddit.com/r/DataHoarder/comments/5yb13m/anyone_...

My home NAS runs btrfs in RAID 5. The key is to use software RAID / LVM to present a single block device to btrfs. That way you never use btrfs's screwed-up RAID 5/6 implementation.

Youden 7y ago

If you use LVM/mdadm for RAID, it's not possible for btrfs to correct checksum mismatches (i.e. protect against bitrot).

brianpgordon 7y ago
That's a good point, though Synology (my brand of NAS) claims that they've developed analogous corruption checks operating at the LVM level, so you get the benefits of btrfs (including checksum checks and RAID scrubbing) without having to actually use its RAID implementation. https://www.synology.com/en-global/knowledgebase/DSM/help/DSM/StorageManager/storage_pool_data_scrubbing https://www.synology.com/en-global/knowledgebase/DSM/help/DS...
- Youden 7y ago
  I wasn't actually able to find any real documentation on how Synology's SHR works. Their recovery documentation [0] indicates that SHR is just plain mdadm + LVM and a couple of NAS recovery sites [1,2] indicate the same. In the end I got a Reddit post [3] with a response from a Synology representative who says that the btrfs filesystem will request a read from a redundant copy from mdadm in order to correct checksum errors. I wonder whether this is unique to Synology or whether the change has been upstreamed into the main Linux kernel. [0]: https://www.synology.com/en-global/knowledgebase/DSM/tutorial/Storage/How_can_I_recover_data_from_my_DiskStation_using_a_PC https://www.synology.com/en-global/knowledgebase/DSM/tutoria... [1]: https://support.reclaime.com/kb/article/8-synology-shr-raid/ https://support.reclaime.com/kb/article/8-synology-shr-raid/ [2]: http://www.nas-recovery.com/kb_hybrydraid.php http://www.nas-recovery.com/kb_hybrydraid.php [3]: https://www.reddit.com/r/DataHoarder/comments/5yb13m/anyone_using_synologys_dsm_61_able_to_confirm/ https://www.reddit.com/r/DataHoarder/comments/5yb13m/anyone_...