[Lustre-discuss] Backup of trusted extended attributes

Andreas Dilger adilger at sun.com
Fri Feb 5 01:02:22 PST 2010


On 2010-02-04, at 11:23, Hervé Kergourlay wrote:
> When I create a file on my lustre FS, add acl and a test xattr named  
> "attr1", with the standard tools "attr", there is 2 xattr
>
> santos.root(55) [dev->Bin] attr -l /mnt/mycltlustre/hky/bck/file.txt
> Attribute "lov" has a 56 byte value for /mnt/mycltlustre/hky/bck/ 
> file.txt
> Attribute "attr1" has a 4 byte value for /mnt/mycltlustre/hky/bck/ 
> file.txt
>
> with an own developped tools, there is I can see 2 lustre xattr,  
> trusted.lov and lustre.lov

The lustre.lov and trusted.lov attributes are really the same thing  
internally.  We used to use only trusted.lov, but it is not possible  
for non-root users to read/write this attribute.

> I see some informations on backup where extended attributes are  
> supposed to be backuped and restored
>
> https://bugzilla.lustre.org/show_bug.cgi?id=5716 or in the lustre -  
> operation manual (chapter 15)
>
> But I would like to get more informations about theses two extended  
> attributes. Which role they have (store lustre splitting  
> information, I could imagine), do we need really to backup them ?  
> and restore them ?
> They should be recreated as restoring a file, it's recreating a  
> file ??

It isn't _required_ to backup and restore these attributes if you are  
just creating a tar archive from the mounted lustre filesystem.  If  
they are not specified then the MDS will supply default attributes for  
the file/directory.

If the lustre.lov and/or trusted.lov attributes are backed up/restored  
(as can be done with the patched tar available at  
downloads.lustre.org) then all files will keep the same stripe count  
and stripe size.

> Or perhaps it's linked with the MDS backup, in case of full  
> desaster / recovery.

If you are doing a MDT-filesystem backup on an ldiskfs-type mount of  
the MDT, then it is critical to back up the trusted.lov attributes, or  
your filesystem will contain no data in it when it is restored.


Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.




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