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Storage networking alternatives

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All the old standards -- FC, iSCSI and NAS -- are still going strong, but FCoE and virtualized I/O are waiting in the wings to help remake our storage networks.

Storage networking rarely gets much attention, and it’s frequently overshadowed by the server and storage gear it links together. But there’s renewed interest in storage networking as new or enhanced technologies begin to show up in our data centers. Sure, there’s lots to talk about with new server technologies, virtualization, operating systems and apps, but all those technologies ultimately require a place to store their data, so they rely on storage networking technologies to handle the task.

There’s a wide variety of storage networking technologies, with something to fit every budget and storage requirement. Storage networking technologies continue to advance to meet today’s growing requirements and to anticipate future needs. Some of these techs are proven and being deployed now or in the near-term. Others are relatively new or not yet very well understood, so their future isn’t as clear.

The broad range of storage networks

Storage networking includes direct-attached storage (DAS), network-attached storage (NAS) and storage-area networks (SANs). We’ll look at some of the interface technologies used in storage networking, including the familiar lineup of Fibre Channel (FC), iSCSI and serial-attached SCSI (SAS), and some of the newer or less widely used interfaces

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such as Fibre Channel over Ethernet (FCoE). We’ll need to examine file serving interfaces such as Common Internet File System (CIFS) and Network File System (NFS). Finally, we’ll explore some I/O virtualization technologies that have some interesting possibilities.

There’s often debate about which storage networking interface is the most popular, with predictions of obsolescence for some storage networking interfaces. After checking research firm IDC’s data tracking storage shipments by host interface type, we find that DAS, FC storage, iSCSI storage and NAS are each multibillion dollar businesses and none of them is going away anytime soon. Furthermore, each one is projected to climb significantly in capacity shipped over the next few years.

STORAGE NETWORKING LINGO

Enlarge STORAGE NETWORKING LINGO diagram.

Direct-attached storage

DAS is the most common and best-known type of storage. In a DAS implementation, the host computer has a private connection to the storage and almost always has exclusive ownership of that storage. The implementation is relatively simple and can be very low cost. A potential disadvantage is that the distance between the host computer and storage is frequently limited, such as within a computer chassis or rack/adjacent rack.

However, SAS, traditionally known as a DAS type of interface, is beginning to show some storage networking-type capabilities. SAS switches have come to market recently that provide a relatively simple method for sharing storage among a small number of servers while maintaining the low-latency SAS is known for.

Network-attached storage

NAS devices, also known as file servers, share their storage resources with clients on the network in the form of “file shares” or “mount points.” These clients use network file access protocols such as CIFS/Server Message Block (SMB) or NFS to request files from the file server. Because NAS operates on a network (usually TCP/IP over Ethernet), the storage can be physically distant from the clients.

File servers running Windows, or those that need to share storage with Windows clients, use the CIFS/SMB protocol. Microsoft Corp. has been enhancing this protocol for several years. Windows 7 and Windows Server 2008 R2 use SMB Version 2.1, which has a number of performance improvements over previous versions. Another implementation of the CIFS/ SMB protocol is Samba 3.6, which uses SMB Version 2.0; other implementations of CIFS/SMB use SMB Version 1.0.

File servers running Unix or Linux natively support NFS. There are three major versions of NFS: NFSv2, NFSv3 and NFSv4. NFSv3 seems to be the most commonly deployed version, and it’s adequate for many applications and environments. NFSv4 added performance and security improvements and became a “stateful” protocol. New features in NFSv4.1 include sessions, directory delegation and “Parallel NFS” (pNFS). pNFS was introduced to support clustered servers that allow parallel access to files across multiple servers.

This was first published in October 2011

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