Updated 2019-02-14

Run BWA on the Cluster

Summary

  • Use module avail bwa to see all available versions of bwa on the cluster.
  • To load BWA in your PBS script:
    • Load its dependent module first with module load open64/4.5.1
    • Load BWA (this guide focuses on BWA/0.7.4) with module load BWA/0.7.4
  • To run BWA:
    • In your PBS script, put all lines executing BWA after the module load lines that loads BWA.

Warning

When aligning sequences with multiple threads (or using the -t flag in general) you must set the number of threads to the number of processors you requested. Example: if you requested 8 (2 nodes and 4 proc. per node), you would set the thread option as -t 8

Example PBS Script

#PBS -N bwaTest
#PBS -l nodes=2:ppn=4
#PBS -l walltime=30:00
#PBS -q iw-shared-6
#PBS -j oe
#PBS -o bwaResult.out

cd $PBS_O_WORKDIR
module load open64/4.5.1
module load bwa/0.7.4
bwa aln -t 8 RefSeqbwaidx <sequence file>.txt >  <output file>.txt.bwa
  • The #PBS directives are standard, requesting 30 min of walltime and 2 nodes with 4 cores per node. More on #PBS directives can be found in the PBS guide
  • $PBS_O_WORKDIR is simply a variable that represents the directory you submit the PBS script from. Make sure the .txt sequence file, and any other files you need are in the same directory you put the PBS script in. This line tells the cluster to enter this directory where you have stored the PBS script, and look for all the files for the job. If you use $PBS_O_WORKDIR, you need to have all your files in the same folder as your PBS script otherwise the cluster won't be able to find the files it needs.
  • Output Files, will also show up in the same directory as the PBS script.
  • The module load lines load BWA and its dependent module
  • bwa aln -t 8 executes BWA. It is just a general example line, and BWA has more functionality then just alignment. The point is to show how the -t flag is used. Here, 8 threads are specified after -t, as 8 processors were requested (2 nodes x 4 proc per node)

Submit Job and Check Status

  • Make sure you're in the directory that contains the PBS script, the sequence files, and any other files you need.
  • Submit as normal, with qsub <pbs script name>. In this case qsub bwa.pbs or whatever you called the PBS script. You can name the PBS scripts whatever you want, just keep the .pbs at the end
  • Check job status with qstat -u username3 -n, replacing "username3" with your gt username
  • You can delete the job with qdel 22182721, replacing the number with the jobid returned after running qsub
  • Depending on the resources requested and queue the job is run on, it may take varying amounts of time for the job to start. To estimate the time until the job executes, run showstart 22182721, replacing the number with the jobid returned after running qsub. More helpful commands can be found in this guide

Collecting Results

  • All files created will be in the same folder where your PBS script is (same directory you ran qsub from)
  • The .out file will be found here as well. It contains the results of the job, as well as diagnostics and a report of resources used during the job. If the job fails or doesn't produce the result your were hoping for, the .out file is a great debugging tool.
  • You can transfer the resulting files off the cluster using scp or a file transfer service