4 ms·

Bidirectional auto file sync is a fundamentally broken pattern and I'm tired of pretending it's not. It's just complete chaos with wrong files constantly gettin

Bidirectional auto file sync is a fundamentally broken pattern and I'm tired of pretending it's not. It's just complete chaos with wrong files constantly getting overridden on both ends. I have no clue why people still use it and I'd cut my losses if I were you, either backup to the cloud or pull from it, not both at the same time like an absolute tictac.

lazide 7mo ago
Throw some clock skew into the mix and it’s even more hilarious!
Gud 7mo ago
Why is this downvoted?
- adamsb6 7mo ago
  The insult to tictacs.
babypuncher 7mo ago
I think this is a case of people using bidirectional file sync wrong. The point is to make the most up to date version of a file available across multiple devices, not to act as a backup or for collaboration between multiple users. It works perfectly fine as long as you keep how it works in mind, and probably most importantly don't have multiple users working directly on the same file at once. I've been using these systems for over a decade at this point and never had a problem. And if I ever do have one, my real backup solution has me covered.
- senkora 7mo ago
  +1. It works perfectly if your mental model is: “Every file is only ever written to from a single client, and will be asynchronously made available to all other clients, and after some period of time has elapsed you can safely switch to always writing to the file from a different client”.
  - 01HNNWZ0MV43FF 7mo ago
    Bidirectional file sync is also in hot demand from people who don't know the words, "file", "client", "write", "async", "available", or "time" :P
    - babypuncher 7mo ago
      The fact that lay people can and will use a tool incorrectly does not mean said tool is not useful
  - unsettledturtle 7mo ago
    Yep. See e.g. steam cloud saves, which is literally just Dropbox for your video game save files. Bidi sync is a super common pattern if you look for it, I'm surprised at all the hate it's getting here.
- andrejserafim 7mo ago
  I agree. I use syncthing for syncing phones and laptops. For data like photos, which aren't really updated. It works very nice. And for documents updated by one user, moving between devices is totally seamless. That being said i understand how it works at a high level.
- donmcronald 7mo ago
  > And if I ever do have one, my real backup solution has me covered. What do you use and how do you test / reconcile to make sure it’s not missing files? I find OneDrive extremely hard to deal with because the backup systems don’t seem to be 100% reliable. I think there are a lot of solutions these days that error on the side of claiming success.
omnimus 7mo ago
I also have no clue why people use it. You can build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.
- j1elo 7mo ago
  Wait a moment, you just gave me an idea for a product
- burnte 7mo ago
  1 out of a thousand people might do that, the others will buy the product. That's why people use it, most people don't want to build everything themselves.
  - srdjanr 7mo ago
    It's a reference to https://news.ycombinator.com/item?id=8863 https://news.ycombinator.com/item?id=8863
    - burnte 7mo ago
      LOL I should have remembered. :D Sorry!
    - Dylan16807 7mo ago
      But as usual it forgets the "For a Linux user" part. If we remove the whole linux section and just ask "why not map a folder in Explorer" it's a reasonable question, probably even more reasonable in 2026 than in 2007. The network got faster and more reliable, and the dropbox access got slower.
- PunchyHamster 7mo ago
  Slow as fuck compared to 2 synced dirs
- zymhan 7mo ago
PunchyHamster 7mo ago
It works perfectly fine if you're user that know how it works. I use it with Syncthing and it works coz I know to not edit same file at the same time on 2 devices (my third and fourth device is always on internet so chances propagate reasonably fast even if the 2 devices aren't on on the same time) But the moment that hits normal users, yeah, mess
Aurornis 7mo ago
> I have no clue why people still use it This is an instance of someone familiar with complex file access patterns not understanding the normal use case for these services. The people using these bidirectional sync services want last writer wins behavior. The mild and moderately technical people I work with all get it and work with it. They know how to use the UI to look for old versions if someone accidentally overwrites their file. Your characterization as complete chaos with constant problems does not mesh with the reality of the countless low-tech teams I've seen use Dropbox type services since they were launched.
- Anamon 7mo ago
  This would be half OK if it worked, but you can't trust it to. OneDrive, for instance, has an open bug for years now where it will randomly revert some of your files to a revision from several months earlier. You can detect and recover this from the history, but only if you know that it happened and where, which you usually won't because it happens silently. I only noticed because it happened to an append-only text file I use daily.
  - sunnybeetroot 7mo ago
    Even crazier is one drive has a limit on the total length of a file path, how is this even a thing that exists.
    - ahhhhnoooo 7mo ago
      Unlimited strings are a problem. People will use it as storage. No, I'm not joking. We used to allow arbitrary paths in a cloud API I owned. Within about a month someone had figured out that the cost to store a single byte file was effectively zero, and they could encode arbitrary files into the paths of those things. It wasn't too long before there was a library to do it on Github. We had to put limits on it because otherwise people would store their data in the path, not the file.
      - garaetjjte 7mo ago
Backblaze-Jim 7mo ago
Hello, Jim from Backblaze here. I wanted to offer some insight into what happened with backing up cloud-synced folders. It is true that we recently updated how Backblaze Computer Backup handles cloud-synced folders. This decision was driven by a consistent set of technical issues we were seeing at scale, most of them driven by updates created by third-party sync tools, including unreliable backups and incomplete restores when backing up files managed by third-party sync providers. To give a bit more context on the “why”: these cloud storage providers now rely heavily on OS-level frameworks to manage sync state. On Windows, for example, files are often represented as reparse points via the Cloud Files API. While they can appear local, they are still system-managed placeholders, which makes it difficult to reliably back them up as standard on-disk files. Moreover, we built our product in a way to not backup reparse points for two reasons: 1. We wanted the backup client to be light on the system and only back up needed user-generated files. 2. We wanted the service to be unlimited, so following reparse points would lead to us backing up tons of data in the cloud We’ve made targeted investments where we can, for example, adding support for iCloud Drive by working within Apple’s model and supporting Google Drive, but extending that same level of support to third-party providers like Dropbox or OneDrive is more complex and not included in the current version. We are currently exploring building an add-on that either follows reparse points or backs up the tagged data in another way. We also hear you clearly on the communication gap. Both the sync providers and Backblaze should have been more proactive in notifying customers about a change with this level of impact. Please don't hesitate to reach out to me or our support team directly if you have any questions. https://help.backblaze.com/hc/en-us/requests/new https://help.backblaze.com/hc/en-us/requests/new We are here to help.

lazide 7mo ago

Throw some clock skew into the mix and it’s even more hilarious!

Gud 7mo ago

Why is this downvoted?

adamsb6 7mo ago
The insult to tictacs.

babypuncher 7mo ago

I think this is a case of people using bidirectional file sync wrong. The point is to make the most up to date version of a file available across multiple devices, not to act as a backup or for collaboration between multiple users. It works perfectly fine as long as you keep how it works in mind, and probably most importantly don't have multiple users working directly on the same file at once. I've been using these systems for over a decade at this point and never had a problem. And if I ever do have one, my real backup solution has me covered.

senkora 7mo ago
+1. It works perfectly if your mental model is: “Every file is only ever written to from a single client, and will be asynchronously made available to all other clients, and after some period of time has elapsed you can safely switch to always writing to the file from a different client”.
- 01HNNWZ0MV43FF 7mo ago
  Bidirectional file sync is also in hot demand from people who don't know the words, "file", "client", "write", "async", "available", or "time" :P
  - babypuncher 7mo ago
    The fact that lay people can and will use a tool incorrectly does not mean said tool is not useful
- unsettledturtle 7mo ago
  Yep. See e.g. steam cloud saves, which is literally just Dropbox for your video game save files. Bidi sync is a super common pattern if you look for it, I'm surprised at all the hate it's getting here.
andrejserafim 7mo ago
I agree. I use syncthing for syncing phones and laptops. For data like photos, which aren't really updated. It works very nice. And for documents updated by one user, moving between devices is totally seamless. That being said i understand how it works at a high level.
donmcronald 7mo ago
> And if I ever do have one, my real backup solution has me covered. What do you use and how do you test / reconcile to make sure it’s not missing files? I find OneDrive extremely hard to deal with because the backup systems don’t seem to be 100% reliable. I think there are a lot of solutions these days that error on the side of claiming success.

omnimus 7mo ago

I also have no clue why people use it. You can build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.

j1elo 7mo ago
Wait a moment, you just gave me an idea for a product
burnte 7mo ago
1 out of a thousand people might do that, the others will buy the product. That's why people use it, most people don't want to build everything themselves.
- srdjanr 7mo ago
  It's a reference to https://news.ycombinator.com/item?id=8863 https://news.ycombinator.com/item?id=8863
  - burnte 7mo ago
    LOL I should have remembered. :D Sorry!
  - Dylan16807 7mo ago
    But as usual it forgets the "For a Linux user" part. If we remove the whole linux section and just ask "why not map a folder in Explorer" it's a reasonable question, probably even more reasonable in 2026 than in 2007. The network got faster and more reliable, and the dropbox access got slower.
PunchyHamster 7mo ago
Slow as fuck compared to 2 synced dirs
zymhan 7mo ago

PunchyHamster 7mo ago

It works perfectly fine if you're user that know how it works. I use it with Syncthing and it works coz I know to not edit same file at the same time on 2 devices (my third and fourth device is always on internet so chances propagate reasonably fast even if the 2 devices aren't on on the same time) But the moment that hits normal users, yeah, mess

Aurornis 7mo ago

> I have no clue why people still use it This is an instance of someone familiar with complex file access patterns not understanding the normal use case for these services. The people using these bidirectional sync services want last writer wins behavior. The mild and moderately technical people I work with all get it and work with it. They know how to use the UI to look for old versions if someone accidentally overwrites their file. Your characterization as complete chaos with constant problems does not mesh with the reality of the countless low-tech teams I've seen use Dropbox type services since they were launched.

Anamon 7mo ago
This would be half OK if it worked, but you can't trust it to. OneDrive, for instance, has an open bug for years now where it will randomly revert some of your files to a revision from several months earlier. You can detect and recover this from the history, but only if you know that it happened and where, which you usually won't because it happens silently. I only noticed because it happened to an append-only text file I use daily.
- sunnybeetroot 7mo ago
  Even crazier is one drive has a limit on the total length of a file path, how is this even a thing that exists.
  - ahhhhnoooo 7mo ago
    Unlimited strings are a problem. People will use it as storage. No, I'm not joking. We used to allow arbitrary paths in a cloud API I owned. Within about a month someone had figured out that the cost to store a single byte file was effectively zero, and they could encode arbitrary files into the paths of those things. It wasn't too long before there was a library to do it on Github. We had to put limits on it because otherwise people would store their data in the path, not the file.
    - garaetjjte 7mo ago

Backblaze-Jim 7mo ago

Hello, Jim from Backblaze here. I wanted to offer some insight into what happened with backing up cloud-synced folders. It is true that we recently updated how Backblaze Computer Backup handles cloud-synced folders. This decision was driven by a consistent set of technical issues we were seeing at scale, most of them driven by updates created by third-party sync tools, including unreliable backups and incomplete restores when backing up files managed by third-party sync providers. To give a bit more context on the “why”: these cloud storage providers now rely heavily on OS-level frameworks to manage sync state. On Windows, for example, files are often represented as reparse points via the Cloud Files API. While they can appear local, they are still system-managed placeholders, which makes it difficult to reliably back them up as standard on-disk files. Moreover, we built our product in a way to not backup reparse points for two reasons: 1. We wanted the backup client to be light on the system and only back up needed user-generated files. 2. We wanted the service to be unlimited, so following reparse points would lead to us backing up tons of data in the cloud We’ve made targeted investments where we can, for example, adding support for iCloud Drive by working within Apple’s model and supporting Google Drive, but extending that same level of support to third-party providers like Dropbox or OneDrive is more complex and not included in the current version. We are currently exploring building an add-on that either follows reparse points or backs up the tagged data in another way. We also hear you clearly on the communication gap. Both the sync providers and Backblaze should have been more proactive in notifying customers about a change with this level of impact. Please don't hesitate to reach out to me or our support team directly if you have any questions. https://help.backblaze.com/hc/en-us/requests/new https://help.backblaze.com/hc/en-us/requests/new We are here to help.