Re: Deprecating ext4 support

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RIP ext4.


Allen Samuels
Software Architect, Fellow, Systems and Software Solutions 

2880 Junction Avenue, San Jose, CA 95134
T: +1 408 801 7030| M: +1 408 780 6416
allen.samuels@xxxxxxxxxxx


> -----Original Message-----
> From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Sage Weil
> Sent: Monday, April 11, 2016 2:40 PM
> To: ceph-devel@xxxxxxxxxxxxxxx; ceph-users@xxxxxxxx; ceph-
> maintainers@xxxxxxxx; ceph-announce@xxxxxxxx
> Subject: Deprecating ext4 support
> 
> Hi,
> 
> ext4 has never been recommended, but we did test it.  After Jewel is out,
> we would like explicitly recommend *against* ext4 and stop testing it.
> 
> Why:
> 
> Recently we discovered an issue with the long object name handling that is
> not fixable without rewriting a significant chunk of FileStores filename
> handling.  (There is a limit in the amount of xattr data ext4 can store in the
> inode, which causes problems in LFNIndex.)
> 
> We *could* invest a ton of time rewriting this to fix, but it only affects ext4,
> which we never recommended, and we plan to deprecate FileStore once
> BlueStore is stable anyway, so it seems like a waste of time that would be
> better spent elsewhere.
> 
> Also, by dropping ext4 test coverage in ceph-qa-suite, we can significantly
> improve time/coverage for FileStore on XFS and on BlueStore.
> 
> The long file name handling is problematic anytime someone is storing rados
> objects with long names.  The primary user that does this is RGW, which
> means any RGW cluster using ext4 should recreate their OSDs to use XFS.
> Other librados users could be affected too, though, like users with very long
> rbd image names (e.g., > 100 characters), or custom librados users.
> 
> How:
> 
> To make this change as visible as possible, the plan is to make ceph-osd
> refuse to start if the backend is unable to support the configured max
> object name (osd_max_object_name_len).  The OSD will complain that ext4
> cannot store such an object and refuse to start.  A user who is only using
> RBD might decide they don't need long file names to work and can adjust
> the osd_max_object_name_len setting to something small (say, 64) and run
> successfully.  They would be taking a risk, though, because we would like
> to stop testing on ext4.
> 
> Is this reasonable?  If there significant ext4 users that are unwilling to
> recreate their OSDs, now would be the time to speak up.
> 
> Thanks!
> sage
> 
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