SDP FAQ Frequently Asked Questions
Q1. What is SDP?
SDP stands for "Sockets Direct Protocol". As the name indicates, it is a wire
protocol for direct communication between RDMA hardware and the application sockets layer that enables applications to directly benefit from the
performance benefits derived from RDMA technology.
Q2. What are sockets layer?
Sockets are a standard programming interface used to communicate with TCP/IP
from applications.
Q3. What is the purpose of
SDP?
SDP enables Internet applications to transparently take advantage of the
performance advantages of the RDMA (Remote Direct Memory Access) protocol suite
(RDMAP/DDP/MPA).
Q4. What are the
advantages of SDP?
SDP enables internet applications to take advantage of the low-latency,
high-bandwidth performance benefits of RDMA, including Direct Data Placement and
Kernel Bypass.
Q5. What is SDP replacing?
SDP emulates sockets streaming semantics over the RDMA interface. It does
not replace any component, but instead emulates sockets semantics to allow
applications to gain the performance benefits of RDMA without changing any
application code which relies on sockets today.
Q6. How is WSD related to
SDP?
WinSock Direct Protocol (WSD, a.k.a. WSDP) is the predecessor to SDP.
Support for WSD is currently shipping in Microsoft Server Operating Systems.
Q7. Is the RDMA Consortium
planning any additional specifications?
No, the SDP specification is the final specification produced by the RDMA
Consortium. The delivery of iSER, SDP, the RDMA wire-protocol suite and the
Verbs Specifications complete the family of protocols necessary to enable
deployment of RDMA based networking, Inter-Process Communication (IPC), and
storage infrastructures.
Q8. What is the plan for
the RDMAC now that the specs are complete?
The consortium members will continue to address Errata for the RDMA Consortium
specifications. The members of the RDMAC will continue to work with the
IETF on approval of the RDMA suite of specifications.
Q9. Will the SDP
specification be submitted to the IETF?
Yes, the RDMAC will submit the SDP specification to the IETF as a proposed
informational RFC to increase familiarity of the SDP protocol with the IETF.
Q10. When will RNIC hardware become available?
Specific details on availability of RNIC hardware need to come from RNIC
vendors. In general, we expect RDMA solutions to be available in 2004.
Q11. When will operating systems support SDP?
Specific details on availability of SDP need to come from OS vendors.
Q12. Who should customers contact for information
on RDMA products?
Customers should contact their respective vendors.
iSER and DA Frequently Asked Questions
Q1. What is iSER?
iSER stands for "iSCSI Extensions for RDMA". As the name indicates, it is
an extension of the data transfer model of iSCSI, a storage networking standard
for TCP/IP. iSER enables the iSCSI protocol to take advantage of the direct data
placement technology of the RDMA (Remote Direct Memory Access) protocol suite (RDMAP/DDP/MPA)
publicly released by the RDMA Consortium in October 2002.
Q2. What is the purpose of iSER?
The iSER protocol seeks to increase the connectivity of the iSCSI end nodes so
that implementations can take advantage of the RDMA over TCP/IP protocol suite.
Q3. What are the advantages of iSER?
The iSER data transfer protocol allows iSCSI implementations to have data
transfers which achieve true zero copy behavior - eliminating TCP/IP processing
overhead as network speeds approach 10Gb/s - on generic RDMA network interface
controllers (RNIC), while preserving the compatibility with iSCSI
infrastructure. Also, in an iSCSI/iSER implementation, certain protocol aspects
of iSCSI, such as data integrity management and some error recovery features are
simplified.
Q3a Why is true zero copy
important?
As networking speeds approach 10Gb/s, much of the overhead of processing
networking traffic is related to memory-to-memory copying, particularly at the
receiver. True zero copy eliminates this overhead.
Q3b Is an RNIC the only
way to achieve true zero copy?
No, but other methods of achieving true zero copy in the NIC require the NIC to
become aware of the actual upper layer protocol being utilized (iSCSI, NFS, DAFS
etc.). An RNIC is the only way to achieve true zero copy without upper layer
protocol specific extensions in the NIC itself.
Q4. Is iSCSI being replaced by iSER?
No, in fact, an iSCSI/iSER implementation requires iSCSI components - such as
login negotiation, discovery, boot, security, and authentication including the
PDU formats � defined by the iSCSI specification. As already noted, iSER
is an extension of the data transfer model of the iSCSI protocol, but does not
change the other areas of the iSCSI protocol. One should view iSER only as a
Datamover for the iSCSI protocol.
Q5. Is iSER a new "iSCSI 2.0"?
No, an iSCSI/iSER implementation must be compliant to the same iSCSI protocol
defined by the IETF iSCSI specification. The iSER protocol utilizes an
existing, compatible iSCSI mechanism (login key negotiation) to determine
whether to use iSER or standard iSCSI data transfer models. Other aspects of the
iSCSI protocol (discovery, boot, security, authentication etc.) are left
unchanged. One should view iSER only as a Datamover for the iSCSI protocol.
Q6. What is DA (or Datamover Architecture)?
The Datamover Architecture for iSCSI (DA) specification defines an abstract
model in which the movement of data between iSCSI end nodes is logically
separated from the rest of the iSCSI protocol in order to allow iSCSI to adapt
to innovations available in new IP transports such as RDMA over TCP/IP.
Q7. How is DA related to iSER? [ or vice
versa ]
The iSER protocol is a 揇atamover protocol� as defined in the Datamover
Architecture for iSCSI specification. The iSER protocol thus applies the
Datamover Architecture for iSCSI in extending the data-movement capabilities of
iSCSI to include RDMA. The Datamover Architecture for iSCSI itself is agnostic
about the specifics of iSER or other supporting protocols.
Q8. Why did you have to define two specs -
DA and iSER?
The architectural intent behind each specification is different. The DA
specification defines a logical separation of data movement from the rest of the
iSCSI protocol in a way that is useful for increasing the connectivity of iSCSI
in the future (such as running iSCSI on other RDMA protocols or even running on
SCTP). The iSER protocol specification applies the Datamover Architecture in
defining a specific mapping of iSCSI抯 data movement features to the RDMA
protocol suite released by the RDMA Consortium in October 2002.
Q9. Doesn't the publication of DA and iSER
specs confuse the nascent iSCSI industry?
No. This work extends the connectivity of iSCSI and is a clear demonstration of
the commitment of RDMA Consortium members to the iSCSI technology and its
advancement. The involvement of several individuals involved in the IETF
iSCSI specification effort also reinforces the complementary nature of iSCSI, DA
and iSER specifications.
Q10. Is the RDMA Consortium advising iSCSI users to move to
iSCSI/iSER-based solutions?
No. The iSER protocol definition is aimed at making iSCSI more pervasive
and is not meant to advise the customers on specific solutions. We expect
each customer to choose a solution that best fits their particular needs.
Q11. What is the roadmap for DA and iSER specs?
The iSER and DA specifications have been released by the RDMA Consortium and are
suitable for industry implementation today. The RDMA Consortium members will
maintain the specifications for any errata discovered during product
implementation. The specifications have also been forwarded to the IETF for
their consideration. Further development of DA and iSER specifications and their
eventual roadmap will be decided by the IETF.
Q12. Is iSER ready for product development?
Yes, the member companies of the RDMA Consortium regard the iSER specification
as suitable for iSCSI/iSER product implementation at the time of the iSER
specification release from the RDMA Consortium.
Q13. What about the interoperability problems between iSCSI
end nodes and the new iSCSI/iSER end nodes?
We do not expect any interoperability problems between iSCSI end nodes and iSCSI/iSER
end nodes. The iSER functionality extends the iSCSI protocol via standard
iSCSI architectural elements (login key negotiation) defined by the iSCSI
specification so that each end node is clearly aware of the mode of operation of
the other end node. Furthermore, the design of the iSER protocol requires
a node which supports iSCSI/iSER to be capable of providing iSCSI protocol login
service compliant with the current iSCSI specification, and to move into the
iSER mode as may be determined necessary during the login negotiation.
Therefore, new iSCSI/iSER implementations should be easily integrated with
current iSCSI networks.
Q14. Does iSER need a special RDMA-capable NIC (RNIC) design?
No. The iSER protocol is designed with an explicit intent to allow iSER to
run on any generic off-the-shelf RNIC. An equally important design goal
also was to allow innovations from vendors who seek to more tightly integrate
iSCSI/iSER into the RNIC hardware.
Q15. Why would such integration be important to vendors?
Many vendors want to continue to use their same APIs to the NICs whether or not
they are operating in traditional iSCSI or iSER mode. By integrating the
iSCSI/iSER functions within the RNIC hardware, the operating mode can be
transparent to the End-Node.
Q16. Does iSER work only on RDMA hardware?
The iSER protocol has no such constraints. The iSER protocol as defined,
should work transparently with either a hardware or software RDMA protocol
stack. Note however that an RNIC-based solution is likely to yield better
performance, assuming typical software processing power.
Q17. Does iSER require support for the recently released RDMA
Verbs specification?
No. The iSER protocol specification itself is completely independent of
the Verbs specification. However, an iWARP implementation compliant to the
RDMA Verbs specification will naturally satisfy all the expectations of the iSER
protocol in the most efficient manner.
Q18. Does iSCSI/iSER code running on an RNIC perform better
than an offloaded iSCSI NIC?
The relative performance depends on the specific iSCSI/iSER/RNIC design versus
the iSCSI NIC design. The iSER specification allows iSCSI end nodes to
take advantage of generic RDMA and data placement technologies, but equally
well-performing iSCSI NIC-based designs are feasible.
Q19. How does iSCSI/iSER with an RNIC position itself against
an iSCSI NIC?
The iSER Datamover is envisioned to be implemented in an iSCSI software
environment which exploits an RNIC, and can thereby offer performance
improvement and reduced overhead to the iSCSI software implementation.
iSCSI implementations that have been included in hardware, which are known as
iSCSI NICs, do not require iSER type of functions since they already do direct
memory placement, have the TCP/IP processing offloaded, have often been tailored
to the needs of iSCSI and tuned to produce the best possible performance.
The iSER specification was intended to permit both types of implementations to
co-exist, and thereby bring the compelling features of iSCSI to all platforms
with as low overhead as possible.
RDMA Consortium FAQs April 29, 2003
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 RMDACmembersApr29.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抯 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 揤erbs� 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抰 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.
