Lustre discuss - Feb 2010 - Backup of trusted extended attributes

I would like to get informations about some specific lustre extended 
attributes backup and restore

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

santos.root(56) [dev->Bin] tina_xattr -tst_num 1 -path_src 
/mnt/mycltlustre/hky/bck/file.txt
I "Vos:tst_stat"[3]Stat Posix
"/mnt/mycltlustre/hky/bck/file.txt"
I "Vos:tst_stat"[9]
I "Vos:tst_stat"[9]xattr list size: 58
I "Vos:tst_stat"[9]
I "Vos:tst_stat"[9]xattr name[0] = trusted.lov
I "Vos:tst_stat"[11]  size: 56
I "Vos:tst_stat"[9]xattr name[1] = system.posix_acl_access
I "Vos:tst_stat"[11]  size: 44
I "Vos:tst_stat"[9]xattr name[2] = user.attr1
I "Vos:tst_stat"[11]  size: 4
I "Vos:tst_stat"[9]xattr name[3] = lustre.lov
I "Vos:tst_stat"[11]  size: 56


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 ??

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

my lustre config

santos.root(57) [dev->Bin] uname -a
Linux santos 2.6.18-128.7.1.el5_lustre.1.8.1.1 #1 SMP Tue Oct 6 05:48:57 
MDT 2009 x86_64 x86_64 x86_64 GNU/Linux

santos root(58) [dev->Bin] rpm -qa | grep lustre
lustre-modules-1.8.1.1-2.6.18_128.7.1.el5_lustre.1.8.1.1
lustre-1.8.1.1-2.6.18_128.7.1.el5_lustre.1.8.1.1
kernel-ib-1.4.2-2.6.18_128.7.1.el5_lustre.1.8.1.1
kernel-lustre-2.6.18-128.7.1.el5_lustre.1.8.1.1
lustre-ldiskfs-3.0.9-2.6.18_128.7.1.el5_lustre.1.8.1.1

Thanks
Herv?
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On 2010-02-04, at 11:23, Herv? 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.