My 2 cents.
Leave at least 4K inodes, then you get massive improvement on small files (less 3.5K minus whatever you use on xattr)
About blocksize for data, unless you have actual data that suggest that you will actually benefit from smaller than 1MB block, leave there. GPFS uses sublocks where 1/16th of the BS can be allocated to different files, so the "waste" is much less than you think on 1MB and you get the throughput and less structures of much more data blocks.
No warranty at all but I try to do this when the BS talk comes in: (might need some clean up it could not be last note but you get the idea)
find . -type f -name '*' -exec ls -l {} \; > find_ls_files.out
cd /usr/lpp/mmfs/samples/ilm
gcc mmfindUtil_processOutputFile.c -o mmfindUtil_processOutputFile
./mmfind /gpfs/shared -ls -type f > find_ls_files.out

cat find_ls_files.out | awk '{print $5","}' > find_ls_files.out.csv
cat find_ls_files.out | awk '{print $7","}' > find_ls_files.out.csv
    LOAD in octave

FILESIZE = int32 (dlmread ("find_ls_files.out.csv", ","));
    Clean the second column (OPTIONAL as the next clean up will do the same)

FILESIZE(:,[2]) = [];
    If we are on 4K aligment we need to clean the files that go to inodes (WELL not exactly ... extended attributes! so maybe use a lower number!)

    If we are not we need to clean the 0 size files




int32 (var (FILESIZE))
    iqr interquartile range, i.e., the difference between the upper and lower quartile, of the input data.

int32 (iqr (FILESIZE))
    Standard deviation
For some FS with lots of files you might need a rather powerful machine to run the calculations on octave, I never hit anything could not manage on a 64GB RAM Power box. Most of the times it is enough with my laptop.

Ystävällisin terveisin / Kind regards / Saludos cordiales / Salutations

Luis Bolinches
Lab Services

IBM Laajalahdentie 23 (main Entrance) Helsinki, 00330 Finland
Phone: +358 503112585

"If you continually give you will continually have." Anonymous
----- Original message -----
From: Stef Coene <stef.co...@docum.org>
Sent by: gpfsug-discuss-boun...@spectrumscale.org
To: gpfsug main discussion list <gpfsug-discuss@spectrumscale.org>
Subject: Re: [gpfsug-discuss] Blocksize
Date: Thu, Sep 22, 2016 10:30 PM
On 09/22/2016 09:07 PM, J. Eric Wonderley wrote:
> It defaults to 4k:
> mmlsfs testbs8M -i
> flag                value                    description
> ------------------- ------------------------
> -----------------------------------
>  -i                 4096                     Inode size in bytes
> I think you can make as small as 512b.   Gpfs will store very small
> files in the inode.
> Typically you want your average file size to be your blocksize and your
> filesystem has one blocksize and one inodesize.

The files are not small, but around 20 MB on average.
So I calculated with IBM that a 1 MB or 2 MB block size is best.

But I'm not sure if it's better to use a smaller block size for the

The file system is not that large (400 TB) and will hold backup data
from CommVault.

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