Re: Can BTRFS handle XATTRs larger than 4K?

[Austin S Hemmelgarn]

On 2014-12-22 15:04, Richard Sharpe wrote:

On Mon, Dec 22, 2014 at 10:09 AM, Austin S Hemmelgarn
<ahferro...@gmail.com> wrote:

On 2014-12-22 12:27, Richard Sharpe wrote:

On Mon, Dec 22, 2014 at 6:28 AM, Austin S Hemmelgarn
<ahferro...@gmail.com> wrote:

On 2014-12-19 21:07, Richard Sharpe wrote:

Hi folks,

I need a Linux file system that supports XATTRs up to 64K.

Can BTRFS support that or is XFS the only Linux file system with such
support?

At the moment, BTRFS is limited to xattrs that fit inline in the metadata
nodes (so ~3900 bytes for a 4k leafsize).

XFS, however, isn't the only Linux filesystem that supports xattrs that
size.  Assuming that you are using a recent kernel, you can also use such
xattrs on at least:
   * XFS
   * JFS
   * ext4
   * reiserfs (I think, not 100% certain about this one though)
   * OCFS2 (even though it is technically a cluster fs, it can be run
single
node without the clustering)
   * ZFS (IIRC, ZFS supports unlimited xattr size)
   * NTFS (no limit on xattr size, though you should use NTFS-3G instead
of
the in-kernel driver)
   * SquashFS (read-only)
   * HFS+ (Also no limit on xattr size)
Of these, I'd personally suggest using XFS unless you need to be able to
shrink the filesystem, in which case I'd suggest ext4.

Thanks for the info. I hadn't realized that ext4 had lifted the
restriction.

Yeah, it would be nice if there was more clarity in the documentation.

Personally, I'd love to see unlimited length xattr's like NTFS and HFS+ do,
as that would greatly improve interoperability (both Windows and OS X use
xattrs, although they call them 'alternative data streams' and 'forks'
respectively), and provide a higher likelihood that xattrs would start
getting used more.

Well, there is a big difference in the semantics of Alternate Data
Streams (ADSs) and XATTRs.

For example, you can seek on an ADS and read at any offset. You cannot
do that on an XATTR (at least, not with the semantics provided by the
UNIX interface.)

I'm not trying to say the semantics are identical, just that the functionality is pretty similar. A better way to put it would be that xattrs are an extremely limited form of ADS/Forks.

smime.p7s
Description: S/MIME Cryptographic Signature