[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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