EX-7681 scripts: Compression estimate script

EX-7681 scripts: Compression estimate script

ll_compression_scan is a simple tool which can be run on any
Linux system to estimate the space usage reduction from the
Lustre Client Side Data Compression (CSDC) feature with
particular compression settings (algorithm, chunk size,
and compression level).

When run on one or more directories, it will recursively
examine a percentage of files under that directory, sampling
data in those files to estimate how the files will compress.

This tools samples data throughout the file, so it should
avoid problems with poor estimates for files with headers
which differ from the bulk data in the file.

However, if the directory tree is particularly imbalanced,
with a few large uncompressible files in one directory, and
many small files in other directories, then scanning a small
percentage of files may give a misleading compression estimate.
Sampling a larger percentage of files will improve this.

This tool requires the lz4, lzop, and gzip utilities to
be installed in order to test those compression types.
(lzop is the command line utility for lzo compression)

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I092f9608553eba10bacfcc3c4a3fafc9a454c287
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51333
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Colin Faber <cfaber@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>