  An experiment to search for mu-e conversion named COMET is being constructed
at J-PARC. The experiment will be carried out using a two-stage approach of
Phase-I and Phase-II. The data taking system of Phase-I is developed based on
common network technology. The data taking system consists of two kinds of
networks. One is a front-end network. Its network bundles around twenty
front-end devices that have a 1-Gb optical network port. And a front-end
computer accepts data from the devices via its network. The other is a back-end
network that collects all event fragments from the front-end computers using a
10-Gb network. We used a low price 1Gb/10Gb optical network switch for the
front-end network. And direct connection between the front-end PC and an event
building PC using 10-Gb optical network devices was used for the back-end
network. The event building PC has ten 10-Gb network ports. And each network
port of the event building PC is connected to the front-end PC's port without
using a network switch. We evaluated data taking performance with an event
building on these two kinds of networks. The event building throughput of the
front-end network achieved 337 MiB/s. And the event building throughput of the
back-end networks achieved 1.2 GiB/s. It means that we could reduce the
construction cost of the data taking network using this structure without
deteriorating performance. Moreover, we evaluated the writing speed of the
local storage RAID disk system connected to a back-end PC by a SAS interface,
and a long-distance network copy from the experiment location to the lasting
storage.
