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Date: Mon, 28 Oct 2013 11:40:18 -0400
From: Ric Wheeler <rwheeler@redhat.com>
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To: "Myklebust, Trond" <Trond.Myklebust@netapp.com>,
        Christoph Anton Mitterer <calestyo@scientia.net>
CC: Mailing List Linux NFS <linux-nfs@vger.kernel.org>,
        Dr Fields James Bruce <bfields@fieldses.org>
Subject: Re: XATTRs in NFS?
References: <1382560643.6924.12.camel@heisenberg.scientia.net> <EFB2CFAD-FACC-401D-BF0C-1C573B23A873@netapp.com> <1382624000.6907.8.camel@heisenberg.scientia.net> <E0F4C952-02DE-4778-A779-FB7AE111EC46@netapp.com> <1382630468.6907.58.camel@heisenberg.scientia.net> <625CAA34-BD6C-4283-86D0-3F8B460D54D0@netapp.com> <1382635350.6907.83.camel@heisenberg.scientia.net> <20131025140846.GB20497@fieldses.org> <1382807547.29041.12.camel@heisenberg.scientia.net> <20131027191512.GA31322@fieldses.org> <1382911068.6932.20.camel@heisenberg.scientia.net> <8DB0D7A2-BA2A-4001-A01C-D498C777B243@netapp.com> <1382920068.6932.46.camel@heisenberg.scientia.net> <2E672741-FE4F-4287-8D00-B7634A71709E@netapp.com>
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On 10/27/2013 08:44 PM, Myklebust, Trond wrote:
> On Oct 27, 2013, at 8:27 PM, Christoph Anton Mitterer <calestyo@scientia.net> wrote:
>
>> On Mon, 2013-10-28 at 00:17 +0000, Myklebust, Trond wrote:
>>> ...and if the checksums are any good, then all you need to do to
>>> substitute a database is to realise that a good data checksum is
>>> invariant under renames.
>> Don't quite see what you mean...
>>
>> Sure the checksums stay the same, but consider you have many millions of
>> files, and you moved them around and thus the paths in the DB are
>> incorrect... verifying the files will become very much a pain in the
>> a**, especially when multiple files don't verify anymore.
>>
>> Or what if you have many small similar files, where errors could lead to
>> a checksum that was a correct one for another file,... when the paths
>> are no longer valid you cannot know if this was a correct file or not.
> If you have lots of small files, and you really do need to associate them uniquely with the checksum, then try something like:
>
> 	ln <filename> /path/to/database/<SHA512 identifier>.<inode number>
>
> Hard links and inode numbers are also generally invariant under 'mv'.
>
> Trond--
>

Then you end up with large directories and an extra name per inode that needs to 
be stored and extra lookups for each file when you do a whole file system crawl.

Certainly not as easy as adding and xattrs with that information :)

Ric