SCSI Target Research Articles

Design, Implementation, and Evaluation of a NUMA-Aware Cache for iSCSI Storage Servers

In an iSCSI based storage area network, target hosts serve concurrent I/O requests from initiators to achieve both high throughput and low latency. Existing iSCSI leverages the OS page cache to ensure data sharing and reuse. However, the non-uniform memory access (NUMA) architecture introduces another dimension of complexity, i.e., asymmetric memory access in multi-core and many-core platforms. Within a NUMA platform, an iSCSI target often dispatches an access request with a cache hit to an I/O thread remote to cached data, and thus cannot fully utilize multi-core systems. We encounter this problem in the context of ultra high-speed data transfer between two iSCSI storage systems, during which inferior NUMA remote memory access lags behind available high network bandwidth, and thereby becomes a bottleneck of the entire end-to-end data transfer path. We design a NUMA-aware cache mechanism to align cache memory with local NUMA nodes and threads, and then schedule I/O requests to those threads that are local to the data being accessed. This NUMA-aware solution results in lower access latency and higher system throughput. We implement a cache system within the Linux SCSI target framework, and evaluated it on our NUMA-based iSCSI testbed. Experimental results show the NUMA-aware cache can significantly improve the performance of iSCSI as measured by several benchmark tools and confirm its viability in data intensive applications and real-life workloads.

SCST를 이용한 All Flash Array 스토리지 가상화

SCST(The generic SCSI target subsystem for Linux) enables developers to make SCSI target storage and supports various SCSI network protocol such as iSCSI, FC, SRP. In this paper, we propose storage virtualization method using SCST and virtualize all flash array as high performance storage through 4Gb Fiber Channel, 10Gb Ethernet and 40Gb Infiniband and evaluate their performance, respectively. Experimental result shows that 40Gb infiniband network appliance have better performance than others. In case of sequential/random read, 40Gb infiniband network appliance shows 78% and 79% of local all flash array performance attached to SCSI target system. In case of sequential/random write, it shows 83% and 88% of local flash array performance attached to SCSI target system.

Design and Implementation of SCSI Target Emulator

A SCSI target emulator is used in a storage area network (SAN) environment to simulate the behavior of a SCSI target for processing and responding to I/O requests issued by initiators. The SCSI target emulator works with general storage devices with multiple transport protocols. The target emulator utilizes a protocol conversion module that translates the SCSI protocols to a variety of storage devices and implements the multi-RAID-level configuration and storage visualization functions. Moreover, the target emulator implements RAM caching, multi-queuing, and request merging to effectively improve the I/O response speed of the general storage devices. The throughput and average response times of the target emulator for block sizes of 4 KB to 128 KB are 150% faster for reads and 67% faster for writes than the existing emulator. With a block size of 16 KB, the I/O latency of the target emulator is only about 20% that of the existing emulator.

Design and Implementation of an SAN System Based on the Fiber Channel Protocol

With the increasing demand for vast storage repositories, network storage has become important for mass data storage and processing, telescopic addressing and availability, and the quality of service and security of data storage. This situation demands the emergence of new technology in the data storage field. In this paper, TH-MSNS, a SAN system, is introduced. This system was designed and implemented based on the fiber channel protocol and its I/O route was tested. This paper introduces some of the key techniques in the network storage system, including an SCSI simulating target, intelligent and uniform storage management architecture, and the processing flow of the read/write commands. The software for the new storage area network system was implemented as a module in the kernel mode to improve its efficiency. The SCSI target adopts a layered design and standardized interface, which is compatible with various types of SCSI devices and can use different network protocols. The storage management software adopts distributed architecture, which enables higher interoperability and compatibility with various kinds of management protocols. TH-MSNS boasts characteristics such as high adaptability, high efficiency, high scalability, and high compatibility and is easy to maintain.

Design and Implementation of a Storage Virtualization System Based on SCSI Target Simulator in SAN

The ideal storage virtualization system is compatible with all operating systems in storage area networks (SANs). However, current storage systems on clustered hosts and multiple operating systems are not practical. This paper presents a storage virtualization system based on a SCSI target simulator in a SAN to solve these problems. This storage virtualization system runs in the target hosts of the SAN, dynamically stores the physical information, and uses the mapping table method to modify the SCSI command addresses. The system uses the bitmap technique to manage the free space. The storage virtualization system provides various functions, such as logical volume resizing, data mirroring, and snapshots, and is compatible with clustered hosts and multiple operating systems, such as Windows NT and RedHat.

내장형 리눅스 기반 RAID 시스템의 구현 및 성능평가

본 논문에서는 내장형 리눅스를 이용한 RAID 시스템의 하드웨어 구현 방법을 제시하고 성능을 측정하여 본 시스템의 장단점을 제시한다. 파이버 채널 디스크와 호스트와의정합을 위하여 세 개리 파이버 채널 제어기를 포함하는 하드웨어를 설계 제작하였으며, 이하드웨어 위에 내장형 리눅스를 이식하고 RAID 소프트웨어를 구현하였다. RAID 기능을 위하여 SCSI 목표 모드 디바이스 드라이버와 목표 모드 SCSI 모듈을 구현하여 호스트 컴퓨터에게 SCSI 블록 디바이스를 제공한다. 또한 RAID의 기능을 위하여 리눅스의 Multi-device 모듈을 사용하였고, 높은 성능을 제공하기 위하여 Multi-device 모듈과 목표 모드 SCSI 모듈의 사이에서 연동하는 데이터 캐쉬 모듈을 구현하였다. 리눅스의 RAID 5 모듈을 수정하여, 읽기 성능을 대폭 향상시켰다. 벤치마크는 새로운 RAID 5모듈이 기존의방법보다 전체적인 성능에서 우수함을 보여준다. In this article, we present, design, and implement a software and hardware for an embedded RAID system. The merits and drawbacks of our system are presented by performance evaluation. The proposed hardware system consists of three fibre channel controllers for the interface with fibre channel disks and hosts. Embedded Linux in which a RAID software is implemented is ported to the hardware. A SCSI target mode device driver and a target mode SCSI module are designed for that our RAID system is considered as a block device to a host computer. Linux Multi-device is used as RAID functions of this system. A data cache module is implemented for high performance and the interconnection between Linux Multi-device and the target mode SCSI module. The RAID 5 module of Multi-device is modified for improvement of read performance. The benchmark shows that the new RAID 5 module is superior to the original one in overall performance.