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Forum Discussion
How does bitrot protection actually work?
I understand the concept, but am curious how it is actually implemented on 6.2.0
I leave it on. Even if file errors can't be repaired, it will at least warn if when it finds something wrong. That might be a false alarm, but still it seems better to get the warning. Though honestly, I think that silent bitrot is quite rare, and its not something I'm particularly concerned about in my OS 4 NAS. One reason I leave it on is just to see if it ever finds anything...
The cost of bitrot protection itself is that btrfs checksums are enabled. So they are checked during file reads, and updated during file writes. There might be a small performance hit on the RN516 - its easy enough to measure any performance impact, since you can create two shares; enabling on one but not the other.
Creating snapshots is always near-instantaneous. Any performance problems they create happen later on, when files in the main share are modified. Then files in the main share get fragmented - and that fragmentation eventually migrates to the snapshots. I leave daily snapshots enabled on most shares despite that possibility. But most of my files aren't modified in place, and I do have defrag, balance, scrubs, and disk checks scheduled in the maintenance schedule (each is run once every three months on each volume).
But if you do have files that are frequently modified in place (downloading torrents, SQL databases, or something like that), then you will want to turn bitrot protection off on those shares. That's becaue Netgear links CoW with BTRFS checksum protection, the GUI doesn't control them independently. The problem is the CoW fragmentation, not the checksum overhead.
To your specific questions:
-bitrot protection by itself does not cause extra wear and tear on the disk. If you end up with fragmentation, then the disks will do more seeking when you read the files, and the balance and defrag maintenance tasks will likely take longer to complete. I don't think that hurts disk life, at least I've never seen studies that claim that.
-snapshots always share file datablocks with each other and the parent share. Bitrot protection doesn't change that. If bitrot protection is off, then CoW is turned on before every snapshot is taken, and turned off after the snapshot completes. If bitrot protection is on, then CoW is on all the time.
The cost of bitrot protection itself is that btrfs checksums are enabled. So they are checked during file reads, and updated during file writes. There might be a small performance hit on the RN516 - its easy enough to measure any performance impact, since you can create two shares; enabling on one but not the other.
Creating snapshots is always near-instantaneous. Any performance problems they create happen later on, when files in the main share are modified. Then files in the main share get fragmented - and that fragmentation eventually migrates to the snapshots. I leave daily snapshots enabled on most shares despite that possibility. But most of my files aren't modified in place, and I do have defrag, balance, scrubs, and disk checks scheduled in the maintenance schedule (each is run once every three months on each volume).
But if you do have files that are frequently modified in place (downloading torrents, SQL databases, or something like that), then you will want to turn bitrot protection off on those shares. That's becaue Netgear links CoW with BTRFS checksum protection, the GUI doesn't control them independently. The problem is the CoW fragmentation, not the checksum overhead.
To your specific questions:
-bitrot protection by itself does not cause extra wear and tear on the disk. If you end up with fragmentation, then the disks will do more seeking when you read the files, and the balance and defrag maintenance tasks will likely take longer to complete. I don't think that hurts disk life, at least I've never seen studies that claim that.
-snapshots always share file datablocks with each other and the parent share. Bitrot protection doesn't change that. If bitrot protection is off, then CoW is turned on before every snapshot is taken, and turned off after the snapshot completes. If bitrot protection is on, then CoW is on all the time.
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