Specifications

Myricom offers 10 Gb/s transfer rates, large receive off-loading, automatic checksum generation, and
an open-source API for software interfacing (as well as open-source, Linux-friendly drivers).
2.4 Software Considerations
As a low-cost alternative to available commercial data capture options, it was desired to avoid
proprietary technologies and their consequent licensing royalties. As a result, the software of the
MCS-DR (including its operating system) is based exclusively on public domain and open source
software.
The reception of UDP datagrams and actual recording of UDP datagrams occur in different
portions of the MCS-DR PC’s data path. The first of these, the “Receive” portion, is responsible
for moving data from the network adapter into the application’s memory space. At the hardware
level, the Ethernet adapter uses DMA
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transfers to place packet data into system memory. The act
of receiving from the socket copies the data into an intermediate buffer where it is then removed by
the “Write” portion of the data path as it writes the data to the hard drive array. Because of the
magnitude of the transfer rates involved, efficiency and economic use of the CPU and memory is
critical. Consequently, the data is only copied once from the time it arrives in system memory until
the time it is written to the hard drives. Tests (See Section 3) have shown that the system supports
transferring data this way at data rates exceeding 450 MiB/s, and that the performance bottleneck
of the system, as expected, is with the hard drives themselves.
3 Testing and Verification
Several key aspects of the prototype system have been characterized, and have been tested to ensure
they meet the requirements set forth in the “MCS Subsystem Definition” [1].
3.1 Hard Drive Performance
The draft design of the MCS-DR PC included Seagate’s 7200.11 series of 1 TB drives, but problems
with meeting the required rates prompted us to use Seagate’s SV35.5 series of 1 TB drives instead.
With the 7200.11 series drives having a maximum sustained transfer rate of 120 MiB/s, and with five
2
Direct Memory Access
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