General NAS Information
NAS devices generally fall into four categories:
- Single drive diskful
These come with drives installed (usually not replaceable or upgradable) and usually have USB 2.0 ports to support expansion via external USB drives. There are many feature variations including built-in FTP and HTTP servers, BitTorrent clients, USB print servers, streaming media servers and backup utilities. Older models have ATA/IDE drives, while newer products use faster SATA drives. - Single drive diskless (BYOD)
These Bring Your Own Drive products accept 3.5″ IDE or SATA drives and are a good way to save money by reusing a drive left over from upgrading a PC’s internal storage. There are also models that accept external USB drives. Features are similar to those in diskful products. - Multi drive diskful
The two advantages of multi-drive NASes are more storage space and RAID – a technology that can provide protection from inevitable disk failure. The key disadvantage is cost, which can be managed by purchasing BYOD products and models supporting fewer drives. You’ll find the same feature sets as in single-drive products (with the exception of RAID). - Multi drive diskless (BYOD)
These products combine the potential cost-savings of BYOD with the feature and functional advantages of multiple drives.
Most all NASes support the SMB/CIFS protocol, which is also supported by most operating systems. So whether your computer is running Windows, Mac OS, Linux or other OS, your machine should be able to access a NASes shares. Most all NASes have web-based administration, so you should also be able to access the controls needed to set the NAS up the way you want it.
The main gotcha is that products tend to come with Windows-only utilities that help you initially find the NAS and change its IP address to match your network. So if you’re not running Windows, you may need to probe around a bit to find your NAS’ initial IP address. Fortunately, most NASes come set to automatically acquire their IP address settings via DHCP, so that reduces the range of possible addresses.
Understanding Performance
The key performance criteria for NASes are read and write throughput. Other specifications that you might focus on for selecting a naked hard drive such as access time, seek time, etc. are generally masked by the overhead of moving data across a network. Factors that do affect throughput include network connection speed, file size and file record size.
The other factor that affects NAS performance is your computer’s operating system and RAM size. Today’s OSes try to use RAM caching (reading and writing to system memory instead of disk storage) as much as possible to avoid performance slowdowns. The more RAM you have and the smaller the file size(s) that you’re dealing with, the more likely that the OS will be able to find what it needs in speedy memory instead of having to go out to (much) slower disk.
We use iozone as our performance test tool, with the procedure described here. Iozone can profile a file system’s performance over a wide range of record and file sizes. But over time we’ve found that it is best to restrict the data that we present to one record size (64 KB) and a small range of file sizes. But even with the reduced data set, iozone results can still be confusing because they often show performance that is faster than the LAN connection’s maximum speed.
The simple answer is that any time that you see NAS performance that is higher than the maximum LAN connection speed, you are looking at cached performance. If you are most interested in what the hardware-limited performance is, concentrate on the write performance at file sizes above 64 MB. While NAS performance continues to improve, our experience has shown that this is where most NASes begin to show their hardware performance limit.