[Lustre-discuss] Restoration of mds is of a different size!

Dilger, Andreas andreas.dilger at intel.com
Thu Dec 20 10:15:25 PST 2012


On 2012-12-18, at 16:39, "Jason Brooks" <brookjas at ohsu.edu> wrote:

> I am currently using lustre 1.8.  I am relatively new with lustre.  At the moment, I am trying to move an mds/mgs system from one disk to another.
> 
> I used the version of tar modified by whamcloud in order to dump and restore the filesytem.  I used mkfs.lustre to create a new mds/mgs filesystem on my /dev/sdc.  I then I mounted the old mds at /mnt/mdsold and the new mds at /mnt/mdsnew using filesystem type "ldiskfs"
> 
> I replicated the filesystem with the following command sequence:
> 
> cd /mnt/mdsold && tar —sparse —xattrs –cf - . | (cd /mnt/mdsnew && tar —sparse —xattrs –xvpf -) 

Looks correct. 

> 
> However, look at the output of df:
> 
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sdd              2.3T  7.9G  2.1T   1% /mnt/mdsold
> /dev/sdc              815G  3.1G  765G   1% /mnt/mdsnew
> 
> 
> Now, why would the new filesystem use 3.1 gigabytes when the old one takes up 7.9G?

Perhaps different inode size, or fewer total inodes?

> =======================
> 
> Side note question: I have used the same version of tar to get a file-level backup of my mds: 
> 
> tar —xattrs —sparse –cf - . >sdd.tar
> 
> The file created was 61 gigabytes in size.
> 
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sdd              2.3T  7.9G  2.1T   1% /mnt/mdsold
> 
> Why is this?  Do the attributes take up extra space?

Tar is padding each file up to 20kB or something like that. 

Cheers, Andreas


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