[tahoe-lafs-trac-stream] [tahoe-lafs] #1325: make `tahoe backup` keep more filesystem metadata

[tahoe-lafs]

#1325: make `tahoe backup` keep more filesystem metadata
-------------------------+-------------------------------------------------
     Reporter:  chrysn   |      Owner:  nobody
         Type:           |     Status:  new
  enhancement            |  Milestone:  undecided
     Priority:  major    |    Version:  1.8.1
    Component:  unknown  |   Keywords:  tahoe-backup metadata symlink
   Resolution:           |  hardlink
Launchpad Bug:           |
-------------------------+-------------------------------------------------
Changes (by amontero):

 * cc: amontero@… (added)


Old description:

> there is a number of probems due to which `tahoe backup` can not replace
> rsync style backups yet. the core of the problem is that tahoe-lafs can
> not keep all the information that is stored in a posix style file system.
> the issues i see are:
>
> * ctime/mtime is not saved
> * symlinks can not be saved (compare ticket #641, which has been around
> for two years)
> * other special files can not be saved (devices etc)
> * user, group and permissions are not saved
> * acls are not saved
>
> i am aware that tahoe has its own ways of dealing with permissions, that
> it has its own time stamps, and that directories work in a way that every
> directory entry is kind of a link anyway, but that's not the point --
> it's about being able to restore a disk's contents from a backup.
>
> from my point of view, symlinks, times and user/group/permissions are the
> most important of these; device files are nowadays created on a ramdisk
> on the fly anyway, and acl users know the problem well enough to have
> their workarouds (afair this is an issue with most backup systems).
>
> implementation-wise, i guess that most if not all of this can be stored
> in the directory as additional information.
>
> if it is possible in trac, i suggest all related bugs to be marked as
> "blocking" this bug.
>
> is this something that is realistic to achieve for tahoe-lafs?

New description:

 there is a number of probems due to which `tahoe backup` can not replace
 rsync style backups yet. the core of the problem is that tahoe-lafs can
 not keep all the information that is stored in a posix style file system.
 the issues i see are:

 * ctime/mtime is not saved
 * symlinks can not be saved (compare ticket #641, which has been around
 for two years)
 * other special files can not be saved (devices etc)
 * user, group and permissions are not saved
 * acls are not saved

 i am aware that tahoe has its own ways of dealing with permissions, that
 it has its own time stamps, and that directories work in a way that every
 directory entry is kind of a link anyway, but that's not the point -- it's
 about being able to restore a disk's contents from a backup.

 from my point of view, symlinks, times and user/group/permissions are the
 most important of these; device files are nowadays created on a ramdisk on
 the fly anyway, and acl users know the problem well enough to have their
 workarouds (afair this is an issue with most backup systems).

 implementation-wise, i guess that most if not all of this can be stored in
 the directory as additional information.

 if it is possible in trac, i suggest all related bugs to be marked as
 "blocking" this bug.

 is this something that is realistic to achieve for tahoe-lafs?

--

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1325#comment:5>
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