Occupation excessive when copy files to ISILON

First, about determinate the amount of space usage on OneFS, take a look in the KB 16635 support.emc.com/kb/16635

(..)

To view the space used to store data in a specified directory, run the following command replacing  with the path to the directory that you want to

measure:

du -sSHAk /ifs/

For example, the command and output for the  directory is: /ifs/data

du -sSHAk /ifs/data

71913088 /ifs/data

To view the space used to store and protect data in a specified directory, run the following command replacing  with the path to the directory that you

want to measure:

du -sSHk /ifs/

For example, the command and output for the  directory is: /ifs/data

du -sSHk /ifs/data

110838453 /ifs/data

(..)

Second, the amount of require space for parity is based on number of nodes in the cluster, size of files and protection level configured (default level is N+2:1).

To have a start point, take a look in the OneFS Administration Guide, Chapter 14 -  Data layout with FlexProtect and in the paper docu42429_White-Paper_-High-Availability-and-Data-Protection-with-EMC-isilon-Scale-Out-NAS.

Pay attention that files with smaller size then 128 KB are mirrored 2x. So, a directory with a huge amount of small files, can use a considerable amount of space to protect data.