Many people who don't have their heads stuck inside their PCs all day get confused about how much memory they have (which we technical people label RAM) and how much storage they have, which we techies generally label "disk space".
Many's the time I have helped a friend or family member who is "running out of memory" and found that the issue is more about their storage than their RAM. Nowadays, with a cheap computer running 1GB, 2GB or even more memory, this is less common, but it seems no matter how much disk space we put in our computers, we're always running out. Family photos, videos, games that come on multiple DVDs, movie libraries - soon even the largest 2TB disks seem restrictive.
I Want More!
Techies always brag about how easy it is to add more storage to their PCs, servers or networks. And it's expected that basic storage is second nature to the desktop and server teams at most businesses.
But to the home users, the junior techies who are just getting started, and sometimes even to experienced desktop and server engineers there are an amazing array of different storage options. Here's a mind-boggling list of acronyms that apply to storage and related technologies - all of which came to mind in less than 60 seconds:
- SD (and MiniSD, MicroSD)
- CompactFlash
- USB
- Firewire/1394
- IDE
- SATA
- DAS
- SAS
- RAID
- Array
- NAS
- SAN
- iSCSI
- FC (Fibre Channel)
- FCoE (Fibre Channel over Ethernet)
With such an array of choices, what should I get? What's best for me?
Types of Storage - DAS, NAS and SAN
Broadly speaking, the types of storage available can be grouped into three different types of storage, based on the way computers connect to the storage, the way in which data is stored and the number of computers that can access the disks at the same time
DAS - Direct Attached Storage
DAS is the collective name for storage that is plugged directly into a single computer or device (like a camera or mobile phone). You can't go out and buy a "DAS" - at least not by that name. But if you bought yourself a single hard disk (SATA, USB and Firewire are good examples) with the idea of plugging it into a single computer at any one time, or a CompactFlash card for your camera, you bought DAS.
DAS is usually the simplest form of storage - both in terms of connecting it and setting it up, and is almost always the cheapest way to add storage, especially to a single computer. The downside is performance and reliability. USB disks are limited to about 30 Megabytes per second, and single SATA disks to around 60 Megabytes per second, in the best cases. In the worst cases, even the fastest SATA disks can slow to 15 or 20 Megabytes per second.
DAS is also applied to servers, where special controllers and multiple disks together provide better performance (80 or 100 Megabytes per second is not uncommon).
NAS - Network Attached Storage
NAS is the next step "up" the storage tree from DAS. NAS devices plug into a network (such as the wired or wireless networks used in many homes and most businesses). Small NAS devices are an easy way for people to add storage for their files without opening up the computer case, or if the computer case is already full. These small NAS devices often have space for just one hard disk, and sometimes also have the option of connecting to a computer using USB.
Small NAS devices often manage even slower performance than USB and SATA disks, because the tiny processor inside the box cannot uise both the disk and the network at the same time, and because the network limits the amount of data that can be sent (for example, a 100Mbit connection can deliver about 10 Megabytes per second).
Larger NAS devices use multiple disks at the same time (usually with RAID to provide redundancy) to provide fast shared disk space to multiple computers at the same time. Larger NAS have Gigabit Ethernet and even multiple Gigabit Ethernet connections, and can supply up to 100 Megabytes of data every second. Larger NAS devices often resemble servers that have a single purpose - storing files.
NAS differs from its cousin, the SAN, by storing files (such as a letter to your aunt, a picture from your holidays or a movie) instead of storing data blocks. NAS devices understand the concept of a file or a directory (folder), where a SAN sees only a block of data and that block of data is owned and managed by a different computer.
SAN - Storage Area Networks
The SAN is the top of the heap when it comes to storage. SANs always have multiple hard disks using RAID to provide redundancy - although very rarely a SAN might provide for RAID 0 (no redundancy at all) - and smart controllers with lots of fast memory (RAM) that make these disk systems extremely fast. It's not uncommon for a small SAN to cost $30,000, $50,000 or even $100,000 to buy and install, and such a SAN may offer only a few terabytes of storage.
But when it comes to large databases, large email systems and systems that need to be online and available at all times of the day and night, SANs are unmatched. SANs provide flexibility (for example, the ability to create a large array of disks and then split up those disks for different systems to access), performance (with high speed processors and lots of memory to store data and fast connections to servers) and resiliency (redundant connections, redundant controllers, redundant disks, battery backup and even dedicated UPS).
SANs understand only blocks of data. This simplicity is part of what makes the SAN a high-performance environment. The computers attached to the SAN are responsible for turning files, emails and databases into small blocks of data (and back again).
Wrap-Up
That wraps up our introduction to the main categories of storage. Join us again next time for a deep dive into Desktop and Notebook storage.
