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Our trusted workhorse Sisu is ending its duty during this month after respectable almost seven years of operation.
Sisu started its service in the autumn of 2012 as a modest 245 Tflop/s system featuring 8-core Intel Sandy Bridge CPUs, reaching its full size in July 2014 with a processor upgrade to 12-core Intel Haswell CPUs and increasing the number of cabinets from 4 to 9. The final configuration totalled 1688 nodes and 1700 Tflop/s theoretical performance. At best, it was ranked the 37th fastest supercomputer in the world (Top500 November 2014 edition). It remained in among the 100 fastest systems in the world for three years, dropping to position #107 in the November 2017 list.
Throughout its service, Sisu proved itself as a very stable and performant system. The only major downtime took place when there was a major disaster that took down the shared Lustre filesystem.
During the course of years, Sisu provided over 1.7 billion core hours for Finnish researchers, playing a major role in several success stories in scientific computing in Finland. Just a couple of examples:
In addition to being a highly utilized and useful Tier-1 resource, it acted as a stepping stone for several projects that obtained the heavily competed PRACE Tier-0 access on the Piz Daint system in Switzerland and other largest European supercomputers. Without a credible national Tier-1 resource, establishing the skills and capacities for using Tier-0 resources would be hard if not impossible.
Sisu also spearheaded several technical solutions. It was among the first Cray XC supercomputers in the world with the new Aries interconnect. In the second phase it was equipped with Intel’s Haswell processors weeks before they had been officially released. It also heralded a change in hosting for CSC. Instead of the machine being placed in Espoo in conjunction with the CSC offices, it was located in an old papermill in Kajaani. This change has brought major environmental and cost benefits, and has been the foundation for hosting much larger machines.
Sisu was the fastest computer in Finland throughout its career, until last month when CSC’s new cluster system Puhti took over the title. Puhti will be complemented by the end of this year by Sisu’s direct successor Mahti, which will again hold the crown for some time. Puhti is currently under piloting use and becomes generally available during August, Mahti at the beginning of next year. Sisu has done its duty now and we wish it a happy retirement. Hats off!