5 ms·

> From what I’ve heard, BTRFS has a crazy long list of defects where it’ll lock up or corrupt data if you so much as look at it wrong The list cannot be crazy

> From what I’ve heard, BTRFS has a crazy long list of defects where it’ll lock up or corrupt data if you so much as look at it wrong The list cannot be crazy long if Synology uses it for their NASes.

yjftsjthsd-h 3y ago
> The list cannot be crazy long if Synology uses it for their NASes. Synology uses a hybrid BTRFS+mdadm arrangement specifically to deal with reliability problems with BTRFS RAID: https://kb.synology.com/en-us/DSM/tutorial/What_was_the_RAID_implementation_for_Btrfs_File_System_on_SynologyNAS https://kb.synology.com/en-us/DSM/tutorial/What_was_the_RAID...
- wolletd 3y ago
  Which is kind of the point. BTRFS only has issues with RAID5/6 configurations. Using it as a filesystem for a single disk or partition should be totally fine.
  - Dalewyn 3y ago
    Everything I've read about btrfs's RAID5/6 deficiencies is that it can't tolerate sudden losses of power (aka write hole problem), which I think is fine so long as you are aware of it and implement appropriate safety measures such as a UPS or APU. And besides, if you are doing RAID you are probably concerned with the system's uptime which probably means you will have implemented such measures anyway. Note that, yes, I'm aware most home users either aren't aware (nobody RTFM) or are too lazy/cheap to buy a UPS from Office Depot. So perhaps btrfs is warning people to save them from themselves.
    - dark-star 3y ago
      A UPS will not much improve the reliability against sudden power loss. At least here in Europe it is much more likely that a PSU or other component fails than that the power line is suddenly interrupted. And lost writes are a problem that all filesystems have. I recommend reading the paper "Parity Lost and Parity Regained" by Krioukov at USENIX 08...
    - amaccuish 3y ago
      Kernel panic too...
  - Mister_Snuggles 3y ago
    Anecdotally, this is untrue. Personally, BTRFS is the only filesystem that has ever caused me any data loss or downtime. I was using a single disk, so it should have been the perfect path. At some point the filesystem got into a state where the system would hang when mounting it read/write. I was able to boot off of a USB stick and recover my files, but I was unable to get the filesystem back into a state where it could be mounted read/write. At work, we used to run BTRFS on our VMs as that was the default. Without fail, every VM would eventually get into a state where a regular maintenance process would completely hang the system and prevent it from doing whatever task it was supposed to be doing. Systems that wrote more to their BTRFS filesystems experienced this sooner than ones that didn't write very much, but eventually every VM succumbed to this. Eventually the server team had to rebuild every VM using ext4. I know that anecdotes aren't data, but my experience with BTRFS will keep me from using it for anything even remotely important.
    - grumpyprole 3y ago
      Unfortunately you got what you payed for! :) No one in the Linux world appears to be seriously investing in engineering a robust and reliable filesystem, with e.g. correctness proofs. We have only hobby projects.
      - Mister_Snuggles 3y ago
        At work, this all happened on a commercial Linux distribution which we do pay for. As far as I recall, their support was unable to resolve the issue, hence rebuilding all those VMs. I’m not on the server team, so I don’t know many details, but I was affected by this issue and it caused a lot of grief across the organization. So no, I don’t think we got what we paid for.
        grumpyprole 3y ago
        Are you sure brtfs is supported in production by your commercial Linux distribution? I would be surprised if this is true. RedHat and Ubuntu do not support it.
- frankjr 3y ago
  I know but that's only one important part of what a file system does. If the file system was otherwise totally broken, they wouldn't use it.
tbyehl 3y ago
Notably, Synology's agent-based backup software requires BTRFS but will not back up BTRFS. https://kb.synology.com/tr-tr/DSM/help/ActiveBackup/activebackup_business_requireandlimit?version=7#b_34 https://kb.synology.com/tr-tr/DSM/help/ActiveBackup/activeba...

yjftsjthsd-h 3y ago

> The list cannot be crazy long if Synology uses it for their NASes. Synology uses a hybrid BTRFS+mdadm arrangement specifically to deal with reliability problems with BTRFS RAID: https://kb.synology.com/en-us/DSM/tutorial/What_was_the_RAID_implementation_for_Btrfs_File_System_on_SynologyNAS https://kb.synology.com/en-us/DSM/tutorial/What_was_the_RAID...

wolletd 3y ago
Which is kind of the point. BTRFS only has issues with RAID5/6 configurations. Using it as a filesystem for a single disk or partition should be totally fine.
- Dalewyn 3y ago
  Everything I've read about btrfs's RAID5/6 deficiencies is that it can't tolerate sudden losses of power (aka write hole problem), which I think is fine so long as you are aware of it and implement appropriate safety measures such as a UPS or APU. And besides, if you are doing RAID you are probably concerned with the system's uptime which probably means you will have implemented such measures anyway. Note that, yes, I'm aware most home users either aren't aware (nobody RTFM) or are too lazy/cheap to buy a UPS from Office Depot. So perhaps btrfs is warning people to save them from themselves.
  - dark-star 3y ago
    A UPS will not much improve the reliability against sudden power loss. At least here in Europe it is much more likely that a PSU or other component fails than that the power line is suddenly interrupted. And lost writes are a problem that all filesystems have. I recommend reading the paper "Parity Lost and Parity Regained" by Krioukov at USENIX 08...
  - amaccuish 3y ago
    Kernel panic too...
- Mister_Snuggles 3y ago
  Anecdotally, this is untrue. Personally, BTRFS is the only filesystem that has ever caused me any data loss or downtime. I was using a single disk, so it should have been the perfect path. At some point the filesystem got into a state where the system would hang when mounting it read/write. I was able to boot off of a USB stick and recover my files, but I was unable to get the filesystem back into a state where it could be mounted read/write. At work, we used to run BTRFS on our VMs as that was the default. Without fail, every VM would eventually get into a state where a regular maintenance process would completely hang the system and prevent it from doing whatever task it was supposed to be doing. Systems that wrote more to their BTRFS filesystems experienced this sooner than ones that didn't write very much, but eventually every VM succumbed to this. Eventually the server team had to rebuild every VM using ext4. I know that anecdotes aren't data, but my experience with BTRFS will keep me from using it for anything even remotely important.
  - grumpyprole 3y ago
    Unfortunately you got what you payed for! :) No one in the Linux world appears to be seriously investing in engineering a robust and reliable filesystem, with e.g. correctness proofs. We have only hobby projects.
    - Mister_Snuggles 3y ago
      At work, this all happened on a commercial Linux distribution which we do pay for. As far as I recall, their support was unable to resolve the issue, hence rebuilding all those VMs. I’m not on the server team, so I don’t know many details, but I was affected by this issue and it caused a lot of grief across the organization. So no, I don’t think we got what we paid for.
      - grumpyprole 3y ago
        Are you sure brtfs is supported in production by your commercial Linux distribution? I would be surprised if this is true. RedHat and Ubuntu do not support it.
frankjr 3y ago
I know but that's only one important part of what a file system does. If the file system was otherwise totally broken, they wouldn't use it.

tbyehl 3y ago

Notably, Synology's agent-based backup software requires BTRFS but will not back up BTRFS. https://kb.synology.com/tr-tr/DSM/help/ActiveBackup/activebackup_business_requireandlimit?version=7#b_34 https://kb.synology.com/tr-tr/DSM/help/ActiveBackup/activeba...