Re: Response to Bcachefs Claims

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-08-25 11:22, Vincent Olivier wrote:
> Hi,
>
> I have been using Btrfs for almost a year now with a 16x4TB RAID10 and its 8x4TB RAID0 backup (using incremental snapshots diffs). I have always tried to stay at the latest stable kernel (currently 4.1.6). But I might be moving to Fedora 22 because Centos 7 has significant incompatibilities with the 4.1.x kernel series.
>
> I have seen the news about Bcachefs aiming to be Btrfs-complete while being extX-stable.
>
> What are the chances Bcachefs beats Btrfs at being the Linux kernel's next "official" file system ? I chose Btrfs over ZFS because it seemed like the only "next-gen" heir to ext4/xfs.
>
> I have been having a few problems with Btrfs myself. I have only one that remains unresolved : I haven't found the best way to mount Btrfs at boot time. "LABEL=" won't work for known reasons (I don't understand however why a mount can't do its own "device scan" transparently). "UUID=" won't work for unknown reasons (haven't got a reply on this, maybe it's the same as "LABEL="). And I will use /dev/* in fstab for stability reasons. Right now I'm mounting the fs manually after a "device scan" and picking up the first device that shows up in the "fi show" run. I can "live" with that but I suppose that things like this contribute to the feeling that Btrfs is actually still experimental contrarily to claims that it is production-ready.
>
> For my own sake and other's I would like to maintain (if nobody is already working on that nor needs any help) a centralized human-readable digest of known issues that would be featured prominently on top of the Btrfs wiki. I would merge the Gotchas page and the various known issues pages (including the various multi-device mount gotchas here and there).
>
> Answers ? Comments ? Help ?
First off, I think this is a wonderful idea.  The list of known issues 
isn't always particularly up to date, and isn't as trivial to find as it 
should be.

Secondly, as far as UUID= not working from the kernel commandline, I 
believe it's for the same reason that LABEL= doesn't work consistently. 
  I would like to point out that LABEL= does work if you use a sane 
initramfs (I boot my desktop using it, although I'm only using an 
initramfs because I have root on a pair of LVM volumes), and I _think_ 
it might also work if you pas device= options in the rootoptions= string.

Thirdly, there is one issue that I haven't seen anyone else mention and 
that is not present on any of the wiki pages at last check:
If you try to use BTRFS on top of LVM thin-provisioning (or 
theoretically any dm-thinp setup), and turn off zeroing of newly 
allocated blocks, this can cause BTRFS to have corruption issues.  I 
think this is actually a dm-thinp issue, not a BTRFS one (turning this 
option off does not clear the discard_zeroes_data flag for the device, 
which I would assume that BTRFS trusts), but is still worth mentioning.



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