On 2017年11月22日 05:00, ST wrote: > On Tue, 2017-11-21 at 11:33 -0700, Chris Murphy wrote: >> On Tue, Nov 21, 2017 at 8:29 AM, ST <smntov@xxxxxxxxx> wrote: >>>>>>> I'm trying to use quotas for a simple chrooted sftp setup, limiting >>>>>>> space for each user's subvolume (now for testing to 1M). >>>>>>> >>>>>>> I tried to hit the limit by uploading files and once it comes to the >>>>>>> limit I face following problem: if I try to free space by removing a >>>>>>> file via Linux sftp client (or Filezilla) - I get error: >>>>>>> "Couldn't delete file: Failure" >>>>>>> >>>>>>> Sometimes, but not always, if I repeat it for 3-5 times it does removes >>>>>>> the file at the end. >>>>>>> If I login as root and try to remove the file via SSH I get the error: >>>>>>> "rm: cannot remove 'example.txt': Disk quota exceeded" >>>>>>> >>>>>>> What is the problem? And how can I solve it? >>>>>> >>>>>> Kernel version first. >>>>>> >>>>>> If it's possible, please use latest kernel, at least newer than v4.10, >>>>>> since we have a lot of qgroup reservation related fixes in newer kernel. >>>>>> >>>>>> Then, for small quota, due to the nature of btrfs metadata CoW and >>>>>> relative large default node size (16K), it's quite easy to hit disk >>>>>> quota for metadata. >>>>> >>>>> Yes, but why I get the error specifically on REMOVING a file? Even if I >>>>> hit disk quota - if I free up space - it should be possible, isn't it? >>>> >>>> It's only true for fs modifying its metadata in-place (and use journal >>>> to protect it). >>>> >>>> For fs using metadata CoW, even freeing space needs extra space for new >>>> metadata. >>>> >>> >>> Wait, it doesn't sound like a bug, but rather like a flaw in design. >>> This means - each time a user hits his quota limit he will get stuck >>> without being able to free space?!! >> >> It's a good question if quotas can make it possible for a user to get >> wedged into a situation that will require an admin to temporarily >> raise the quota in order to make file deletion possible. > > Why question? It's a fact. That's what I face right now. > >> This is not a >> design flaw, all COW file systems *add* data when deleting. The >> challenge is how to teach the quota system to act like a hard limit >> for data writes that clearly bust the quota, versus a soft limit that >> tolerates some extra amount above the quota for the purpose of >> eventually deleting data. That's maybe non-trivial. It's not that it's >> a design flaw. Metadata can contain inline data, so how exactly to you >> tell what kinds of writes are permitted (deleting a file) and what >> kind of writes are not (append data to a file, or create new file)? >> >> But for sure the user space tools should prevent setting too low a >> quota limit. If the limit cannot be reasonably expected to work, it >> should be disallowed. So maybe the user space tools need to enforce a >> minimum quota, something like 100MiB, or whatever. >> > > Would you like to open an issue with your enhancement suggestions on the > bug tracker so this case doesn't get forgotten? That's why I ask for the kernel version. IIRC in newer kernel, quota doesn't limit deletion anymore, preventing you from hitting such dilemma. Thanks, Qu > > Thank you! > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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