LHC: Colaba connection

The LHC,where 40 million proton collisions occur a second ¿ comparable to a 4 megapixel photograph being shot 40 million times a second — will produce tens of thousands of gigabytes of data that require about 20 million CDs of storage space each year,not to mention computing power equivalent to about a lakh of the world’s best personal computers. That’s why Nagaraj and Deshpande,in their forties and having spent over two decades with TIFR,are important cogs in a giant computing system that is keeping this data accessible to thousands of researchers across the world. They are the system administrators at what is called a Tier 2 site for the Worldwide LHC Computing Grid,a unique computing system that borrows the computing power of facilities like this one across the world in order to process the mindboggling data being generated by the LHC experiments.

“You may have heard the term ‘dual core’ to describe a normal desktop computer at home. Well,we have 350 cores here,soon to be upgraded to 650 cores,” says Nagaraj. That’s 350 terabytes of data,being pumped into the computers through a 1000 kbps dedicated giant bandwidth. “That’s 1 GB per second,” adds Deshpande.

TIFR’s Tier 2 site (named so for its location in a hierarchy of sites in the grid) has been in the making for two-and-a-half-years now. “Stress tests have been carried out,data is now coming in constantly,there are about 650 jobs going on at any time,so there are jobs in queue,” says Deshpande. “There is a great responsibility on us to ensure that downtime is kept to a minimum,despite any problems that may occur.” This Tier2 has to demonstrate that they can sustain download rates of at least 1.5TB (terabytes) per day from seven different Tier1 sites and upload rates of at least 0.5 TB per day.

Nagaraj likens the grid to an electricity grid. “You plug in your appliance and it works,you don’t care where the power is coming from,” he explains.

Similarly,50 physicists spread across the country (including two groups in TIFR itself,BARC,Delhi University,Shantiniketan and Panjab University) and thousands of others across the world connect to the computing grid using the Internet,access data of their choice ferreted out from the minefield of data and fire their jobs to the grid,getting their results once the computing is done. It’s a virtual computing organization,accessible to those with the mandatory digital signatures.

“In principle,you can allot privilege slots to the 50 Indians who are part of the Compact Muon Solenoid (CBM) experiment,also called the India CMS group,” says Nagaraj,adding that every Tier 2 site reserves some of its resources exclusively to local community members in the experiment.

The engineers at TIFR know these 50 by name,from quarterly meetings held each year; and they even have some idea of the progress the physics researchers are making. “We feel responsible for every user accessing the grid through our Tier 2 site,they can ‘open a ticket on us’ if they encounter any problems. But the feeling of belonging to such a major global event is a huge high,” Nagaraj says.

A senior physicist at TIFR,involved with the analyzing of data from the experiments and sharing responsibilities to keep the Tier 2 site running without glitches,says the Worldwide LHC Computing Grid will someday revolutionise how the world accesses and uses computing power. “At this point,there’s a lot of security involved,each one of us has a digital certificate required for accessing the grid. But in five years,perhaps,it will evolve into something for the common man… that’s how the Internet evolved too,remember?”