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Btrfs is in production all over the damn place, at big corporations and all kinds of different deployments. Synology has their own btrfs setup that they ship to

by jchw 2y ago

Btrfs is in production all over the damn place, at big corporations and all kinds of different deployments. Synology has their own btrfs setup that they ship to customers with their NAS software for example. I found it incredibly annoying the first time I ran out of disk space on btrfs, but many of these points are hyperbolic and honestly just silly. For example, btrfs doesn't really do offline fsck. fsck.btrfs has a zero percent chance of destroying your volume because it does nothing. As for the user space utilities changing... I'm not sure how that demonstrates the filesystem is not production ready. Personally I usually use either XFS or btrfs as my root filesystem. While I've caught some snags with btrfs, I've never lost any data. I don't actually know anyone who has, I've merely just heard about it. And it's not like other well-regarded filesystems have never ran into data loss situations: even OpenZFS recently (about a year ago) uncovered a data-eating bug that called its reliability into question. I'm sure some people will angrily tell me that actually btrfs is shit and the worst thing to ever be created and honestly whatever. I am not passionate about filesystems. Wake me up when there's a better one and it's mainlined. Maybe it will eventually be bcachefs. (Edit: and just to be clear, I do realize bcachefs is mainline and Kent Overstreet considers it to be stable and safe. However, it's still young and it's upstream future has been called into question. For non-technical reasons, but still; it does make me less confident.)

aaronmdjones 2y ago
For example, btrfs doesn't really do offline fsck. fsck.btrfs has a zero percent chance of destroying your volume because it does nothing. fsck.btrfs does indeed do nothing, but that's not the tool they were complaining about. From the btrfs-check(8) manpage: Warning Do not use --repair unless you are advised to do so by a developer or an experienced user, and then only after having accepted that no fsck can successfully repair all types of filesystem corruption. E.g. some other software or hardware bugs can fatally damage a volume. [...] DANGEROUS OPTIONS --repair enable the repair mode and attempt to fix problems where possible Note there’s a warning and 10 second delay when this option is run without --force to give users a chance to think twice before running repair, the warnings in documentation have shown to be insufficient
- jchw 2y ago
  Yes, but that doesn't do the job that a fsck implementation does. fsck is something you stuff into your initrd to do some quick checks/repairs prior to mounting, but btrfs intentionally doesn't need those. If you need btrfs-check, you have probably hit either a catastrophic bug or hardware failure. This is not the same as fsck for some other filesystems. However, ZFS is designed the same way and also has no fsck utility. So whatever point was intended to be made was not, in any case.
shiroiushi 2y ago
>I don't actually know anyone who has, I've merely just heard about it. Well "yarg", a few comments up in this conversation, says he lost all his data to it with the last year. I've seen enough comments like that that I don't see it as a trustworthy filesystem. I never see comments like that about ext4 or ZFS.
- jchw 2y ago
  Contrary to popular belief, people on a forum you happen to participate in are still just strangers. In line with popular belief, anecdotal evidence is not a good basis to form an opinion.
  - shiroiushi 2y ago
    Exactly how do you propose to form an opinion on filesystem reliability then? Do my own testing with thousands of computers over the course of 15 years?
    - jchw 2y ago
      You don't determine what CPUs are fast or reliable by reading forum comments and guessing, why would filesystems be any different? That said, you make a good point. It's actually pretty hard to quantify how "stable" a filesystem is meaningfully. It's not like anyone is doing Jepsen-style analysis of filesystems right now, so the best thing we can go off of is testimony. And right now for btrfs, the two types of data-points are essentially, companies that have been using it in production successfully, and people on the internet saying it sucks. I'm not saying either of those is great, and I am not trying to tell anyone that btrfs is some subjective measure of good. I'm just here to tell people it's apparently stable enough to be used in production... because, well, it's being used in production. Would I argue it is a particularly stable filesystem? No, in large part because it's huge. It's a filesystem with an integrated volume manager, snapshots, transparent compression and much more. Something vastly simpler with a lower surface area and more time in the oven is simply less likely to run into bugs. Would I argue it is perfectly reasonable to use btrfs for your PC? Without question. A home use case with a simple volume setup is exceedingly unlikely to be challenging for btrfs. It has some rough edges, but I don't expect to be any more likely to lose data to btrfs bugs as I expect to lose data from hardware failures. The bottom line is, if you absolutely must not lose data, having proper redundancy and backups is probably a much bigger concern than btrfs bugs for most people.
anonfordays 2y ago
>Synology has their own btrfs setup that they ship to customers with their NAS software for example. Synology infamously/hilariously does not use btrfs as the underlying file system because even they don't trust btrfs's RAID subsystem. Synology uses LVM RAID that is presented to btrfs as a single drive. btrfs isn't managing any of the volumes/disks.
- jchw 2y ago
  Their reason for not using btrfs as a multi-device volume manager is not specified, though it's reasonable to infer that it is because btrfs's own built-in volume management/RAID wasn't suitable. That's not really very surprising: back in ~2016 when Synology started using btrfs, these features were still somewhat nascent even though other parts of the filesystem were starting to become more mature. To this day, btrfs RAID is still pretty limited, and I wouldn't recommend it. (As far as I know, btrfs RAID5/6 is even still considered incomplete upstream.) On the other hand, btrfs subvolumes as a whole are relatively stable, and that and other features are used in Synology DSM and ChromeOS. That said, there's really nothing particularly wrong with using btrfs with another block-level volume manager. I'm sure it seems silly since it's something btrfs ostensibly supports, but filesystem-level redundancy is still one of those things that I think I would generally be afraid to lean on too hard. More traditional RAID at the block level is simply going to be less susceptible to bugs, and it might even be a bit easier to manage. (I've used ZFS raidz before and ran into issues/confusion when trying to manage the zpool. I have nothing but respect for the developers of ZFS but I think the degree to which people portray ZFS as an impeccable specimen of filesystem perfection is a little bit unrealistic, it can be confusing, limited, and even, at least very occasionally, buggy too.)
  - anonfordays 2y ago
    >That's not really very surprising: back in ~2016 when Synology started using btrfs, these features were still somewhat nascent even though other parts of the filesystem were starting to become more mature. btrfs was seven years old at that point and declared "stable" three years before that. ZFS is an example of amazingly written code by awesome engineers. It's simple to manage, scales well, and easy to grok. btrfs sadly will go the wayside once bcachefs reaches maturity. I wouldn't trust btrfs for important data, and neither should you. If you experience data loss on a Synology box, the answer you'll get from them is "tough shit, hope you have backups, and here's a coupon for a new Synology unit."

by jchw 2y ago

aaronmdjones 2y ago

For example, btrfs doesn't really do offline fsck. fsck.btrfs has a zero percent chance of destroying your volume because it does nothing. fsck.btrfs does indeed do nothing, but that's not the tool they were complaining about. From the btrfs-check(8) manpage: Warning Do not use --repair unless you are advised to do so by a developer or an experienced user, and then only after having accepted that no fsck can successfully repair all types of filesystem corruption. E.g. some other software or hardware bugs can fatally damage a volume. [...] DANGEROUS OPTIONS --repair enable the repair mode and attempt to fix problems where possible Note there’s a warning and 10 second delay when this option is run without --force to give users a chance to think twice before running repair, the warnings in documentation have shown to be insufficient

jchw 2y ago
Yes, but that doesn't do the job that a fsck implementation does. fsck is something you stuff into your initrd to do some quick checks/repairs prior to mounting, but btrfs intentionally doesn't need those. If you need btrfs-check, you have probably hit either a catastrophic bug or hardware failure. This is not the same as fsck for some other filesystems. However, ZFS is designed the same way and also has no fsck utility. So whatever point was intended to be made was not, in any case.

shiroiushi 2y ago

>I don't actually know anyone who has, I've merely just heard about it. Well "yarg", a few comments up in this conversation, says he lost all his data to it with the last year. I've seen enough comments like that that I don't see it as a trustworthy filesystem. I never see comments like that about ext4 or ZFS.

jchw 2y ago
Contrary to popular belief, people on a forum you happen to participate in are still just strangers. In line with popular belief, anecdotal evidence is not a good basis to form an opinion.
- shiroiushi 2y ago
  Exactly how do you propose to form an opinion on filesystem reliability then? Do my own testing with thousands of computers over the course of 15 years?
  - jchw 2y ago
    You don't determine what CPUs are fast or reliable by reading forum comments and guessing, why would filesystems be any different? That said, you make a good point. It's actually pretty hard to quantify how "stable" a filesystem is meaningfully. It's not like anyone is doing Jepsen-style analysis of filesystems right now, so the best thing we can go off of is testimony. And right now for btrfs, the two types of data-points are essentially, companies that have been using it in production successfully, and people on the internet saying it sucks. I'm not saying either of those is great, and I am not trying to tell anyone that btrfs is some subjective measure of good. I'm just here to tell people it's apparently stable enough to be used in production... because, well, it's being used in production. Would I argue it is a particularly stable filesystem? No, in large part because it's huge. It's a filesystem with an integrated volume manager, snapshots, transparent compression and much more. Something vastly simpler with a lower surface area and more time in the oven is simply less likely to run into bugs. Would I argue it is perfectly reasonable to use btrfs for your PC? Without question. A home use case with a simple volume setup is exceedingly unlikely to be challenging for btrfs. It has some rough edges, but I don't expect to be any more likely to lose data to btrfs bugs as I expect to lose data from hardware failures. The bottom line is, if you absolutely must not lose data, having proper redundancy and backups is probably a much bigger concern than btrfs bugs for most people.

anonfordays 2y ago

>Synology has their own btrfs setup that they ship to customers with their NAS software for example. Synology infamously/hilariously does not use btrfs as the underlying file system because even they don't trust btrfs's RAID subsystem. Synology uses LVM RAID that is presented to btrfs as a single drive. btrfs isn't managing any of the volumes/disks.

jchw 2y ago
Their reason for not using btrfs as a multi-device volume manager is not specified, though it's reasonable to infer that it is because btrfs's own built-in volume management/RAID wasn't suitable. That's not really very surprising: back in ~2016 when Synology started using btrfs, these features were still somewhat nascent even though other parts of the filesystem were starting to become more mature. To this day, btrfs RAID is still pretty limited, and I wouldn't recommend it. (As far as I know, btrfs RAID5/6 is even still considered incomplete upstream.) On the other hand, btrfs subvolumes as a whole are relatively stable, and that and other features are used in Synology DSM and ChromeOS. That said, there's really nothing particularly wrong with using btrfs with another block-level volume manager. I'm sure it seems silly since it's something btrfs ostensibly supports, but filesystem-level redundancy is still one of those things that I think I would generally be afraid to lean on too hard. More traditional RAID at the block level is simply going to be less susceptible to bugs, and it might even be a bit easier to manage. (I've used ZFS raidz before and ran into issues/confusion when trying to manage the zpool. I have nothing but respect for the developers of ZFS but I think the degree to which people portray ZFS as an impeccable specimen of filesystem perfection is a little bit unrealistic, it can be confusing, limited, and even, at least very occasionally, buggy too.)
- anonfordays 2y ago
  >That's not really very surprising: back in ~2016 when Synology started using btrfs, these features were still somewhat nascent even though other parts of the filesystem were starting to become more mature. btrfs was seven years old at that point and declared "stable" three years before that. ZFS is an example of amazingly written code by awesome engineers. It's simple to manage, scales well, and easy to grok. btrfs sadly will go the wayside once bcachefs reaches maturity. I wouldn't trust btrfs for important data, and neither should you. If you experience data loss on a Synology box, the answer you'll get from them is "tough shit, hope you have backups, and here's a coupon for a new Synology unit."