Download the repo

Whereven on the T2 where you have the output from crab.

git clone https://github.com/Oviedo-PAF/nanoAOD-tools.git

Merge crab output

cd xtools/rootfileReader/

Merge a single dataset into chunks of 2 Gb:

python haddtrees.py ../../CRABOUTPUT/SAMPLE/DATASET/ --outname NAME --maxSize 2000

Merge all the samples in a given production

paython haddtrees.py ../../CRABOUTPUT/ --prod myProd_DDMMYY --maxSize 1000