HPSS file extraction

HPSS (High Performance Storage System) is a mass file storage system for NERSC. Lots of data outputs of E3SM are stored in HPSS.

To see what’s in HPSS, use hsi from any NERSC node
To extract file from HPSS to NERSC, need to use zstash
- load conda and activate the zstash environment
```
  module load python
  conda create -n zstash_env -c e3sm -c conda-forge zstash`
  source activate zstash_env 
```
- then the zstash environment is activated, should see (zstash_env) leading command line
- to extract files, use
```
  zstash extract --hpss=<path to HPSS> [files]
```
Normally the files will be tared in a directory named as 000000.tar, 000001.tar … etc. and there is a index.db file describing what files are tared. The .db file is a database file can’t be read directly. Need to extract to nersc directory first.
To read the .db file, use following command to see the content of the index.db, or other commands
```
sqlite3 zstash/index.db "select * from files;>filelist.txt"
```
Once find the .tar files that contain the E3SM outputs need to be extracted, extract them and then untar them using tar -xvf