[Lustre-discuss] Size of MDT, used space

Andreas Dilger adilger at sun.com
Tue May 13 15:31:36 PDT 2008


On May 13, 2008  19:41 +0200, Thomas Roth wrote:
> I'm still in trouble with numbers: the available, used and necessary 
> space on my MDT:
> According to "lfs df", I have now filled my file system with 115.3 TB.
> All of these files are sized 5 MB. That should be roughly 24 million files.
> For the MDT, "lfs df" reports 28.2 GB used.
> 
> Now I believed that creating a file on Lustre means using one inode on 
> the MDT. Since all of my Lustre partitions were formatted with the 
> default options (all of this is running Lustre v. 1.6.4.3, btw), an 
> inode should eat up 4kB on the MDT partition. Of course, 24 million 
> files times 4 kB gives you 91 GB rather than 28GB.
> Obviously, there is something I missed completely. Perhaps somebody 
> could illuminate me here?
> 
> This issue could also be phrased as "How large should my MDT be to 
> accommodate n TB storage space?" The manual's answer boils down to "= 
> number of files * 4 kB "  (*2 per recommendation). That's how I 
> calculated above - maybe my test system is broken? I can't check on the 
> content of these files, it's just 5MB test files created with the 
> 'stress' utility.

Please provide output of "lfs df" and "lfs df -i" so we can see the
actual numbers.

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




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