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RDMA based Kernel Services

Goals

The original goal of Remote Direct Memory Access (RDMA) technology was to enable efficient user-level communication without involving the OS. With performance critical applications increasingly being deployed in the OS kernel, RDMA is increasingly being used not only for user-level but also for in-kernel applications.

Unlike user-level applications, which perform a limited set of independent tasks, the OS kernel is a large program with a single resource pool. To enable efficient RDMA inside the kernel requires unified management of resources like communication endpoints, buffers used for data transfers, and the kernel virtual address space. Our goal is to develop an RDMA Service Platform (RSP), which manages such resources without performance overheads. In RSP, we provide resource management and a service for remote address descriptor exchange. We developed two network storage protocols over RSP: NFS, a file based network attached storage (NAS) protocol, and iSCSI, a block based storage area network (SAN) protocol.


RDMA Service Platform (RSP)

RDMA Service Platform is the basic building block of RDMA based kernel services. It provides buffer and endpoint management, flow control, and a service for remote memory descriptor exchange. Using RSP, global resource management decisions are possible and multiple kernel services can be built without overallocation or underutilization of allocated resources. RSP defines a generic API for in-kernel services without imposing significant performance overhead. It also defines a generic external service for remote memory descriptor exchange essential for RDMA communication. The goal of our research in RSP is to study the effectiveness of multiple resource management mechanisms and policies when used by multiple kernel based services.

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NFS over RDMA

NFS is arguably the most prevalent NAS protocol. We are currently designing and building an in-kernel RDMA based NFS service (client and server). Our study of this architecture will begin with a thorough evaluation of the performance characteristics of NFS over RDMA (with a comparison to standard NFS over TCP/IP). We will also evaluate the programmability of NAS services over our RDMA Service Platform (see "RSP" above), using NFS over RSP as a case study.

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SCSI over RDMA

SCSI over IP (iSCSI) is a popular SAN protocol. We are currently extending iSCSI to incorporate support for RDMA based transports. Our implementation of iSCSI over RDMA is built on top of RSP. The goal of our research is to evaluate the benefits of RDMA and zero-copy transports as well as design novel caching strategies to improve the performance of the iSCSI protocol over RDMA.

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Publications

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Software

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People

Faculty

 Liviu Iftode

Graduate Students

 Aniruddha Bohra, Steve Smaldone

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