A.4  Case Study: Data Staging

NCSA has an existing cluster where a significant portion of submitted jobs require input data to be staged from an hierarchical storage manager (HSM).  Currently, each user must stage the input data for each job manually before submitting the job.  Also, each job must be intelligent enough to determine if its input data is present before beginning execution.  Not only is this inconvenient for users, it can lead to scheduling inefficiencies as "running" jobs sit idle waiting for input data to arrive. 

NCSA's cluster consists of 100 single processor nodes connected by a switched gigabit network.  The storage manager is a 200 terabyte tape storage system with 4 terabyte disk cache. 

The goals of allowing Moab to manage the data staging requirements of a cluster include:

Efficiency

The scheduler must not start a job until its input data has been staged to the appropriate location.

Adaptation

The scheduler must make intelligent decisions based on the estimated completion time of data staging operations.

Space Allocation

The scheduler must maintain enough free disk space to accommodate the stage-out data of currently running jobs.

Moab supports a STAGEIN resource manager extension that allows the user to specify stage-in requirements for a job.  If this extension is present, Moab will not attempt to start the job until the specified file is present.  Additionally, if a size is given, Moab will wait until the file exists and is at least as big as the specified size. 

Moab will estimate the time required for a staging operation to complete if the BANDWIDTH parameter in moab.cfg is set.  This allows Moab to make properly timed, pre-execution data stage requests from the storage manager. 

The TARGETUSAGE parameter can be used to set the desired storage manager disk cache utilization level.  It should be set below 100% to allow for unexpected external usage and job stage-out files with sizes that are not known in advance. 

A resource manager named hsm will be created to monitor and manage the storage manager load and resources. 

FIX: Where does transfer rate info go???

# configure the storage manager
RMCFG[hsm] TYPE=NATIVE
RMCFG[hsm] RESOURCETYPE=STORAGE TARGETUSAGE=80%

# gives Moab information about the storage manager
RMCFG[hsm] CLUSTERQUERYURL=exec:///$TOOLSDIR/dstage.clusterquery.pl

# allow Moab to check for the existence of a file and its size
RMCFG[hsm] SYSTEMQUERYURL=exec:///$TOOLSDIR/dstage.systemquery.pl

# allow Moab to request a staging operation
RMCFG[hsm] SYSTEMMODIFYURL=exec:///$TOOLSDIR/dstage.systemmodify.pl

The following script files are provided with Moab.  They can be customized to work with any type of data staging solution.  In addition, there are many scripts provided with Moab that work with 3rd party storage solutions without the need for any customization. 

• dstage.clusterquery.pl
• dstage.systemquery.pl
• dstage.systemmodify.pl

More information about these resource manager interfaces can be found in the data staging documentation. 

Moab will make the best use of computing resources when it understands the data staging needs of its jobs and the speed at which staging requests can be met by the storage manager.