[Lustre-discuss] Measuring used space in inodes.

Ashley Pittman ashley at pittman.co.uk
Mon Oct 25 14:36:06 PDT 2010


There is a lot of documentation out there to help in choosing the best inode size for a filesystem however none that I can find about measuring the actually used space in inodes on an existing filesystem.  As an example I have a existing Lustre filesystem where the MDT has a inode size is 512 bytes, the filesystem makes heavy use of ACLs however and MDT performance is below what is expected - the suspicion is that we are overflowing the 512 allowance and having to do two lookups for each file access.  On a related note what happens when there is not enough space in the inode for all the data, is a second inode used or is a block allocated?

Is there a way to measure the space used by the inode for a given file, we are looking at debugfs and the stat command which is giving us some data but it's not clear how to parse this information and calculate the space used.  Some info is shown in the "Blockcount:" field in the stat output but this increases in multiples of 8 and I only see a listing of blocks when it's value is 16 or more.  There are also the "File ACL" and "Directory ACL" fields but these are not always non-zero even when ACLs are used?

The specific FS I'm thinking about typically has 28 ACL on a file and there are 30 OSTS but most files have a default stripe-count of 1, Ideally I'd like a way of seeing a size-distrobution for all inodes in a filesystem though so I could use this as the basis for choosing the inode size.

Ashley.

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Ashley Pittman, Bath, UK.

Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk




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