Q1: Who are the members of the
RDMA Consortium?
A1: The founding members are
Adaptec, Broadcom, Cisco, Dell, EMC, Hewlett-Packard, IBM, Intel, Microsoft and
Network Appliance. Additionally there are over 50 member companies of the RDMA
Consortium, a list of which is available at http://www.rdmaconsortium.org/home/RMDACmembers.htm.
Q2: What is the RDMA
Consortium announcing at this time?
A2: The RDMA Consortium is
announcing completion of version 1.0 of the RDMA Verbs specification. The
completed Verbs specification accompanies the RDMA wire-protocol suite, which
was completed in October of 2002. The
specifications are suitable for first generation industry implementations of
RDMA over TCP solutions and comprise the information required for RDMA hardware
development. The consortium continues
to work on additional protocol specifications to broaden usage of the RDMA
protocol suite which are expected to be completed in 3Q03.
Q3: What is the schedule and
status of the specifications?
A3: Version 1.0 of the RDMA
over TCP wire protocol specifications was completed in October of 2002 and was
forwarded to the IETF where it is now an official work item of the RDDP
workgroup. The RDMA Verbs specification now is complete and has been forwarded
to the IETF for their consideration. Work on additional protocol specifications to broaden usage of the RDMA protocol suite is expected
to be completed in 3Q03.
Q4: What are the
specifications that have been completed to date?
A4: The RDMA Verbs
specification and the suite of three specifications that describe the RDMA over
TCP wire protocol: RDMA Protocol, DDP protocol
and MPA protocol. All four specifications can be retrieved from rdmaconsortium.org.
Q5: What is RDMA over TCP?
A5: Remote Direct Memory Access
is the ability of one computer to directly place information in another
computer’s memory with minimal demands on memory bus bandwidth and CPU
processing overhead, while preserving memory protection semantics. RDMA over
TCP/IP defines the interoperable protocols to support RDMA operations over
standard TCP/IP networks.
Q6: What does it take to
become a RDMA Consortium member?
A6: Information on applying for
membership is available at rdmaconsortium.org.
The RDMA Consortium will accept members according to transparent criteria which
is published on the website.
Q7: Why is RDMA over TCP
important?
A7: Demand for networking
bandwidth and increases in network speeds are growing faster than the
processing power and memory bandwidth of the compute nodes that ultimately must
process the networking traffic. This is especially true as the industry begins
migrating to 10Gigabit Ethernet infrastructures. RDMA over TCP addresses these
issues in two very important ways: first, much of the overhead of protocol
processing can be moved to the Ethernet adapter and second, each incoming network
packet has enough information to allow its data payload to be placed directly
into the correct destination memory location, even when packets arrive out of
order. The direct data placement property of RDMA eliminates intermediate
memory buffering and copying and the associated demands on the memory and
processor resources of the compute nodes, without requiring the addition of
expensive buffer memory on the Ethernet adapter. Additionally, RDMA over TCP/IP uses the existing
IP/Ethernet based network infrastructure.
Q8: What is the relationship
of RDMA over TCP to InfiniBand and VI Architecture?
A8: All three architectures
specify a form of RDMA and have strong similarities. The VI Architecture goal
was to specify RDMA capabilities without specifying the underlying transport.
The InfiniBand architecture improved upon the RDMA capabilities of VI and
specifies an underlying transport and physical layer. RDMA over TCP/IP will
specify an RDMA layer that will interoperate over a standard TCP/IP transport
layer. RDMA over TCP does not specify a physical layer; it will work over
Ethernet, wide area networks (WAN) or any other network where TCP/IP is used.
Q9: What is an RNIC?
A9: An RNIC is an RDMA enabled
NIC (Network Interface Controller). The RNIC provides support for the RDMA over
TCP protocol suite and can include a combination of TCP offload and RDMA
functions in the same network adapter.
Q10: What is the significant of
the RNIC Verbs specification?
A10: The RNIC Verbs
specification provides a standard, semantic interface definition for the
functions performed by an RNIC. It is expected that network adapter vendors
will support the RDMA protocol using the semantics defined by the RNIC
Verbs. It is also expected that
software vendors will interface to RNICs using the semantics defined by the
RNIC Verbs specification. As a result, a standard, semantic RNIC Verbs
definition should accelerate the adoption rate for RNICs.
Q11: How are the RDMA over TCP/IP Verbs related to the InfiniBand
Verbs?
A11: The architectural
interfaces to InfiniBand and RDMA over TCP/IP are both defined by a “Verbs”
interface specification. The Verbs specification developed by the RDMA
Consortium has a large amount of semantic commonality with the InfiniBand
Verbs. The Verbs specification developed by the RDMA Consortium also provides
performance enhancements for some application environments.
Q12: Will RDMA/TCP require
changes to applications to deliver customer benefit?
A12: No. It is expected that
legacy applications will see significant performance advantages using standard
interfaces such as Sockets and storage.
Q13: Will RDMA/TCP require
changes to TCP or other Internet protocols?
A13: No. The RDMA over TCP
specification takes as a requirement that it operate over standard TCP with no
required changes to Internet infrastructure.
Q14: What is the relationship
between TCP offload engines (TOE) and RDMA?
A14: A TCP offload engine is a
specialized (intelligent) network adapter that moves much of the TCP/IP
protocol processing overhead from the host CPU/OS to the network adapter. TCP
Offload Engines reduce much of the TCP/IP protocol processing burden from the
main CPU. However, the ability of performing zero copy of incoming data streams
on a TOE is very dependent on the TOE design, the operating system's
programming interface, and the application's communication model. In many
cases, a TOE doesn’t directly support zero copy of incoming data streams. RDMA
directly supports a zero copy model of incoming data over a wider range of application
environments than a TOE . The combination of TCP offload and RDMA in the same
network adapter is expected to provide an optimal architecture for high speed
networking with the lowest demands on both CPU and memory resources.
Q15: Will RDMA/TCP work over
the Internet?
A15: Absolutely. RDMA is being
layered on top of TCP to specifically work reliably over the Internet. RDMA
does not change TCP's congestion-avoidance mechanisms or security architecture
(IPSEC).
Q16: What is the status of
RDMAC specifications in the IETF?
A16: Information on RDMA over
TCP/IP wire-protocol specifications within the IETF is available at
http://www.ietf.org/html.charters/rddp-charter.html.
Q17: What are the annual dues?
A17: There are no recurring
annual dues. The founding members have committed financial resources sufficient
for specification development and industry review.
Q18: How do I get more
information on RDMA over TCP?
A18: More information on RDMA
over TCP is available at (www.rdmaconsortium.org)
or from individual founder companies.