Learning the ABCs for Network Storage - Part One
NAS Overview
NAS (Network Attached Storage) is just what it says it is--storage attached via your network. The NAS box does all it's communicating with your network/application server via Ethernet using network communications protocols. A NAS box can be any type of file server, RAID box, etc. as long as it can communicate in this fashion. NAS is almost always implemented as an adjunct to DAS and as such, shouldn't really be considered a standalone networking solution.
NAS pros:
NAS installs easily: pull the prepackaged solution out of its shipping carton, plug an Ethernet cable into it, assign an IP address, configure it over the network and you're ready to go. Compared to implementing a SAN, or even adding storage to a DAS server (which is what you're actually doing in a sense) NAS is as easy as pie.
NAS is relatively inexpensive: NAS Boxes come as cheap as Quantum's $500 20GB Snap Server. At the other end of the spectrum you'll find big boys like Network Appliances' $138,000 multi-box 1.9 terabyte F880. That may seem pricey, but compared to a SAN of the same capacity it's chump change.
NAS scales well: As you might've noticed in the previous Pro, there's a NAS box to fit every situation. If you just need 20GB to serve as a local workgroup dumping ground, NAS can accommodate you. If you need terabytes of space for a multimedia farm, NAS will also do the trick.
NAS speed is improving: A traditional knock on NAS is that it's only as fast as your network. Gigabit (125MBps) Ethernet is available today as a drop-in upgrade to properly wired 10/100Mbps networks. It’s a relatively cheap upgrade and backward compatible with your current Cat 5 cables.
NAS crosses OS barriers: Because it does its communications via Ethernet, a competent NAS box can be accessed by virtually any type of server: UNIX, Linux, Windows, Apple. This means you don't have to keep multiple copies of files as with SAN or DAS. The NAS box handles all the file system and translation details.
NAS is easy to manage: Most NAS boxes are managed over the network via a Web browser from any client so you don't have to be at a main console to do your managing or be running a particular OS. Even better, shutting down a NAS box for maintenance doesn't require shutting down the entire network as with DAS.
NAS cons:
Network speed is a limiting factor: The same attached-via-a-network-node model that makes NAS so easy to install and manage means that communications with a NAS box are limited to the speed of your network. Many networks are still 100 megabit per second (100Mbps/12.5MBps) Fast Ethernet and some antiques might still be chugging along at 10Mbps. That pales in comparison with the 33MBps to 160MBps of bandwidth local ATA or SCSI discs provide for DAS servers, or the 125MBps to 250MBps 1 Gigabit or 2 Gigabit Fibre channel SANs offer. However, with Gigabit Ethernet coming into its own and 10 Gigabit on the horizon, network speed will soon be a non-issue.
Network traffic can slow a NAS down and vice versa: Network protocols and interruptions from other network processes will obviously slow down your access to the files on a NAS box. Turning that around, backing up a NAS box can suck up a ton of network bandwidth, strangling other access. One workaround many IT departments have implemented is dedicating a network channel to the NAS box for backup. Most NAS boxes can be backed up locally to eliminate the problem entirely.
Low-level access -- Not!: Applications that don't support the Common Internet File System (CIFS) used by Windows-based networks or Network File System (NFS) won't be able to access files on a NAS box. Applications that rely on block-level access (NAS can generally only serve a file, not parts of one) to disks may also be a problem. Also, NAS boxes don't perform as well with Novell Netware networks or Macs not running the newer OS X.
What to look for in a NAS box:
If you’re interested in a NAS solution, here are some questions you should ask yourself before deciding which box to buy.
1. What network protocols and file systems does it support? Any NAS box you buy should support all the protocols and file systems (NIF, CIFS, AFS, etc) that are in use on your network.
2. What speed Ethernet does it support? If a NAS box only supports 10/100Mbit Ethernet then it's performance won't improve when you upgrade your network to Gigabit Ethernet or beyond. Ideally, your NAS box's Ethernet connection should be upgradeable.
3. What OS runs the box? Some NAS servers run Linux, some run Windows NT, some use proprietary operating systems. There are arguments for each: Linux is free, not at the mercy of corporate whims, and always being upgraded. A proprietary OS is built from scratch for the specific purpose of running a NAS box and is undoubtedly leaner and faster, however, you are at the mercy of the vendor for upgrades and bug fixes. Windows NT is common, not going anywhere and lets you use your existing software applications for backup, etc. but you're at Microsoft's mercy and it's not optimized for NAS.
4. How fast is it internally? The technology inside NAS varies wildly and can drastically impact performance. Cheaper boxes might be using slower ATA66 technology. More expensive boxes may use optimized Fibre Channel to link storage devices together. Your faster NAS boxes have multiple Ethernet connections to increase bandwidth.
5. How scalable is it? Low-end boxes either aren't upgradeable or are only be upgradeable in the 100s of Gigabytes. High-end servers are upgradeable in terabytes.
6. Can it leverage your backup devices? Tape drives and other backup devices are expensive. A NAS box with a SCSI port may let you leverage your existing backup equipment and therefore save you money.
Next week: SAN, virtualization, and how to choose between DAS, NAS, and SAN