Storage Area Networks vs. Local RAID Arrays?

Noxx asks: "My department is purchasing several new servers for an intranet website project. We are under pressure to store our content on an existing Storage Area Network accessed over a fibre connection rather than on a local RAID-5 array, to cut purchasing costs on the new hardware. Have any Slashdot readers evaluated the pros and cons between the two storage technologies, and are there any points of concern we should address? How does performance compare between the two, and is this a proper use of the SAN? If multiple servers access the same content from the SAN, is the possibility of introducing a single point of failure (ie: the SAN crashes) a valid concern?"

Comments

SAN is probably better

[crow]

Generally, you will find that using a SAN is better. The sort of equipment that is deployed in a SAN is typically higher-end than what you would get with a stand-alone RAID array.

You probably also get a number of other advantages. Your SAN is probably already backed up. Your SAN is likely already part of any disaster recovery plan.

And while you could view the SAN as a single point of failure, you could also view your local RAID array as a single point of failure. Any decent SAN implementation has redundancy at every level.

Of course, I'm biased, as I work for EMC, a big SAN company.

You probably need to sit down with your IT people and discuss with them exactly how the SAN is set up. You'll probably find that it has more than enough reliability and performance for any web server application.

NAS is better for many things

[smoon]

NAS, or "Network attached Storage" is often better for maintaing large collections of data to be accessed by multiple computers. You can simulate NAS by exporting some filesystems via NFS (Unix) or CIFS (Windows). Network Appliance "Filers" are said to be very good. On the lower end are the Maxtor MaxAttach and Quantum Snap! devices.

The big advantage to NAS is that dozens of web servers can mount the NAS volume and all serve up the same content. Developers, Administrators, etc. can also mount the NAS volume and do updates etc. Compared to a SAN and buying a fibre channel card, cabling, switch ports, etc. for anything but non-essential components gets very expensive very quickly. Although a previous poster indicated that multiple computers can mount the same SAN volume, It's much more difficult than with NAS since you're essentially operating at the same level as a SCSI bus, wheras with NAS you're operating via TCP/IP.

A Fibre Channel SAN is good for multiple computers running I/O intensive processes, e.g. a SQL database. It's also good as a foundation for clusters since (usually) LUNs can be re-mapped w/out a reboot. SANs really shine for fully redundant storage as well -- multiple loops, switches, controllers, etc.

Many products in both categories suffer in support for backup -- the typical low-end devices require you to mount the data on a server then use a server-attached tape device. Some products feature built-in tape drives or offer ways to back up the entire storage unit to a fibre channel attached tape drive, however this option tends to get very expensive very quickly.

One major bonus in the backup arena is the "snapshot" feature many products have (SAN or NAS). This lets you freeze 'the drive' so that no updates happen to the drive for your backup, but the system still stays up and allows updates. See vendor propaganda for more details.