09 March 2012

Busy afternoon for ATLAS Storage at the RAL T1

Lunchtime on the 8th March 2012 was a busy time for the disk servers in the ATLAS instance of CASTOR at the Tier1 at RAL. Servers were delivering approximately 45Gbps as a source:

FTS controlled transfers at this as controlled by the RAL FTS WAN transfers were negligible; since the majority of "WAN" transfer via FTS (RAL) system were actually an intra-CASTOR transfer.

"WAN Rate"

"Intra-CASTOR" rate shown below shows that of the 4-5GB/s only 2.5Gbps is internal FTS traffic. ( ~5% of traffic.)

However this is only ~1/3 of the outbound traffic over the WAN. The other traffic is controlled by other FTS servers.
ATLAS aggregate this into the following ATLAS specific plot:
This shows the outbound traffic was actually 625MB/s (~5Gbps)
 ATLAS have a graph showing amount of data processed . This peaked at over 8TB in one hour.

However 8TB/hour is approximately 25Gbps
So what was using the remaining bandwidth...

Well we also need to include traffic from disk servers to tape servers (which are LAN transfers that neither ATLAS nor FTS know about. This rate can be seen here:

This shows there is an extra 600MB/s (~5Gbps) of rate unaccounted for. With FTS+WN+Tape network loads; the known bandwidth usage is 35Gbps. As a rough estimation, this explains how the majority of the bandwidth was used.