[Lustre-discuss] performance: hard vs. soft links

Andreas Dilger adilger at whamcloud.com
Fri May 25 09:19:27 PDT 2012

On 2012-05-25, at 5:06, Michael Kluge <Michael.Kluge at tu-dresden.de> wrote:
> for creating hard links instead of soft links (1.6.7, 1000 links created by 
> one process, all in the same subdir, the node is behind one lnet router) I see 
> about 25% overhead (time) on the client side. Is this OK/normal/expected? 
> Lustre probably needs to increment some ref. counter on the link target if 
> hard links are used?

Hard links are only directory entries with refcounts on the target inode, so that when the last link to an inode is removed the inode will be deleted. 

Symlinks are inodes with a string that points to the original name. They are not recounted on the target, but require a new inode to be allocated for each one. 

It isn't obvious which one would be slower, since they both have some overhead.

Is your sample size large enough?  1000 may only take 1s to complete and may not provide consistent results. 

Cheers, Andreas

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