[tahoe-dev] BackupDB proposal

Nathan nejucomo at gmail.com
Thu May 29 18:57:37 PDT 2008

On Thu, May 29, 2008 at 12:12 PM, Brian Warner
<warner-tahoe at allmydata.com> wrote:


> It would be really cool if the filesystem were to provide us with a reliable
> indicator of whether the file had changed: a version number, or a strong hash
> of the contents. Maybe HFS+ or ZFS or reiser4 or one of the other fancy new
> ones could provide this feature.

I completely agree.  -and since Tahoe is a fancy new filesystem, it
would be nice if it provided this feature.  ;-)

I requested this a while ago in [1], but wanted to clarify a point
about implementation trickiness:

Although somehow providing a SHA1 would be a user-friendly way to
implement this feature, something more "natural" to tahoe could also
work.  For example if there is a readily available merkle tree result,
exposing that through the webapi can achieve the same effect (with a
little more implementation work on the client).  A CHK is such a
natural result which is already exposed to a client.  It'd be nice if
the feature were general to mutable files/directories also.

Even if it isn't feasible for a disk-based backup implementation, it
is a general feature which may come in handy in other ways.  Some
examples are see [2], systems which already use tools like tripwire,
and any new wapi client which can afford caching computations.


[1] http://allmydata.org/trac/tahoe/ticket/280
[2] http://allmydata.org/trac/tahoe/ticket/89

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