Performance Comparison of iSCSI and NFS IP Storage

Performance Comparison of iSCSI and NFS IP Storage protocols.
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Introduction.
Currently two major approaches to file transfer in a storage network exist. Those approaches are so-called "block I/O" and "file I/O".

For the "block IO" approach, the SCSI protocol is the protocol of choice in the storage management arena. Different transport mechanisms, such as parallel SCSI, Fibre Channel (FC), or Internet SCSI (iSCSI) can be used to transfer SCSI protocol data.

SCSI is a mature and well established protocol used for fast access to storage devices. However, it has serious drawbacks, such as distance (several meters) and scalability (15 devices on a bus) limitations. While Fibre Channel (FC) has overcome some of SCSI drawbacks and became currently dominant protocol for SAN, it also has certain capability limitations. A high cost for FC SAN installation and maintenance, lack of security and access control mechanisms, lacking long distance capabilities (<500m regular, <10km with special and costly equipment), makes emerging protocols, such iSCSI and Infiniband (IBA), serious competitors to FC for a certain set of applications.

Among emerging storage protocols, iSCSI is a very promising mechanism for SCSI command transfer using IP network. Based on TCP/IP protocol, iSCSI uses TCP flow control, congestion control, segmentation mechanisms, and it is built upon the IP addressing and discovery mechanisms. Using existing gigabit Ethernet infrastructure, iSCSI can provide gigabit speeds comparable to FC and will have 10Gbit speeds available in the near future. iSCSI is more scalable with respect to the number of storage devices in the SAN then FC or IBA due to its addressing and discovery mechanisms. iSCSI is better suited then FC or IBA for deployment over WAN, since it leverages existing IP infra-structure, which has practically no distance limitations and has well-understood network security mechanisms.

For the "file IO" approach, NFS and CIFS protocols are practically the only protocols used today for network file system access. Like iSCSI, these protocols are based on TCP/IP protocol. The ability of NFS/CIFS to represent storage appliance as a local file system accessible by clients, allows file shared storage access. However, there is number of applications that do not require file sharing. Moreover, there are applications, whose performance is significantly degraded when accessing data using "file IO" approach, like databases and similar transaction-oriented applications. However, those applications do require IP connectivity between servers and clients, particularly in certain redundant failover configurations.

The purpose of this work is compare the performance of iSCSI and NFS using benchmarks that emulate different storage access patterns, such as streaming writes and reads (Bonnie), database access (IOgen) and small file access (PostMark).