[Lustre-discuss] Size of MDT, used space

[Thomas Roth]

Andreas Dilger wrote:
> 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.
> 



Ok, I'm attaching these two files with the output. You'll notice some 
OSTs with  a lower fill level: these OSS had some hardware problems 
during the production of my (now counted) 22.7 million files.
Greetings,
Thomas

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