What is StashCache?
StashCache is a data service for OSG which transparently caches data near compute sites for faster delivery to active grid jobs. The standard practice of using HTCondor file transfer or http to move data files to grid sites can be inefficient for certain workflows. StashCache uses a distributed network filesystem (based on XRootD proxy caching) which provides an alternative method for transferring input files to compute sites. It is implemented through a handful of strategically-distributed sites which provide caching of the input data files.
When to use StashCache
StashCache typically outperforms other methods in the following cases:
- Jobs require large data files (> 500 MB)
- The same data files are used repeatedly for many separate jobs
How to use StashCache
StashCache is available at all OSG sites where OASIS is mounted and can be used for both job input and output.
Transfer job input from StashCache
To use it for transferring files to active jobs:
1) Copy the data files required for the job(s) into your
/public Stash directory which is mounted on the OSG Connect login node here:
2) Include the following lines in the job's submit script to indicate that StashCache is required and the necessary modules are available:
+WantsStashCache = true requirements = OSGVO_OS_STRING == "RHEL 7" && Arch == "X86_64" && HAS_MODULES == True
3) Use the 'stashcp' command-line tool in the job wrapper script to transfer necessary data files to the compute host.
First load the stashcp module:
module load stashcache
Then transfer your data:
stashcp /osgconnect/public/<userid>/<stash_data_file_path> <target_location>
Note how the
/public directory is mapped to the
/osgconnect/public namespace under StashCache. For example, if the data file is located at
/public/<userid\>/samples/sample01.dat, then the
stashcp command to transfer this file into your current working directory on the compute host would be:
stashcp /osgconnect/public/<userid>/samples/sample01.dat .
Transfer job output to StashCache
To transfer job output to StashCache after your analysis:
1) Ensure that your job's submit script indicates the necessary requirements to make
stashcp available by including the following lines:
+WantsStashCache = true
requirements = OSGVO_OS_STRING == "RHEL 7" && Arch == "X86_64" && HAS_MODULES == True
stashcp to transfer the data files back to StashCache. You will need to prepend your stash location with
stash:// as follows:
module load stashcache stashcp <file_name> stash:///osgconnect/public/<userid>/<stash_data_file_path>
For example, if you wish to transfer
output.dat to the directory
/public/<userid\>/output/. then the
stashcp command would be:
stashcp output.dat stash:///osgconnect/public/<xuserid>/output/output.txt
More usage options are described in the stashcp help message:
$ stashcp -h Usage: stashcp [options] source destination Options: -h, --help show this help message and exit -d, --debug debug -r recursively copy --closest Return the closest cache and exit -c CACHE, --cache=CACHE Cache to use -j CACHES_JSON, --caches-json=CACHES_JSON The JSON file containing the list of caches --methods=METHODS Comma separated list of methods to try, in order. Default: cvmfs,xrootd,http -t TOKEN, --token=TOKEN Token file to use for reading and/or writing
This page was updated on Aug 07, 2020 at 16:30 from start/data/stashcache.md.