Veritas-bu

[Veritas-bu] Restoring files with Hard Links

2000-02-16 14:08:19
Subject: [Veritas-bu] Restoring files with Hard Links
From: Ray Locklear ray.locklear AT ptech DOT com
Date: Wed, 16 Feb 2000 14:08:19 -0500
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Upon further investigation, we found that NetBackup did in fact back up
the hard link first and then backed up the name of the original file.  So,
we had to restore the hard link in order to get the data.

Thanks so much for you help!

Ray

Jonathan Meyer wrote:

> Ray,
>
> my understanding is that netbackup handles hard links in a way which
> can lead to problems if you are not expecting it.
>
> Somewhere in the manual there is a section that describes the
> behaviors for handling links.
>
> I usually think of soft links as pointers and hard links as additional
> names for the same file.  At the file system level, all hard links to
> a file are equal.
>
> From the netbackup perspective all hard links are not equal.  I think
> what happens is that when netbackup traverses the filesystem, it
> writes the file to tape when it encounters the first hard link to it.
> When it encounters additional hard links to the same file, netbackup
> records them as pointers to the first copy on tape.
>
> Handling hard links in this way can lead to at least two types of
> problems.  If you try to restore a single file, and the name you ask
> for was not the hard link that netbackup encountered first when doing
> the backup, then netbackup will not restore the file.  This happens
> because at that point on the tape netbackup has found a pointer
> instead of your data.
>
> There is also some way to do a restore where you end up with two
> separate files even though the originals were hardlinks to each other.
> I cannot remember the mechanism for causing this problem at the
> moment.
>
> Going back to your original email, I was suprised at the work around
> you mentioned which was to restore to an alternate path.  I would not
> have thought that would help.  What I think should solve the problem
> would be to restore all of the names which were links to the file you
> want.  I would do the restore to an alternate location, and I think if
> you try all the names for the file, you should get your data.
>
> One other note, I believe these behaviors for handling links are
> behaviors inherited from GNU tar, which netbackup uses to write its
> data.
>
> --------------------------------------------------
> Jonathan Meyer
> (781)398-6594
> UNIX Systems Administrator
> Paramtric Technology Corporation
> --------------------------------------------------
>
> _______________________________________________
> Veritas-bu maillist  -  Veritas-bu AT mailman.eng.auburn DOT edu
> http://mailman.eng.auburn.edu/mailman/listinfo/veritas-bu

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