Hard-Drive Interfaces
These days there are so many different types of storage connectors, it’s easy to get confused and choose something that doesn’t fit your requirements. Hopefully this will help explain the different types of interfaces and their strengths and weaknesses, so you can work out what best suits your needs.
Internal Drive Interfaces:
These are the native hard drive interfaces that connect the actual hard-disk to the enclosure, or to inside your desktop machine.
SCSI: This is still the king for absolute speed in RAID arrays, but it is very expensive per GB compared to IDE/SATA, and can be a bit temperamental - so unless you have vast amounts of money to burn, or very particular circumstances, I’d definitely stay away from it for archiving purposes.
ATA/IDE: This is the traditional hard drive found in most computers, and is a perfectly good choice. It’s relatively cheap and you may already own a few which could be a good reason for sticking with it.
Serial ATA (SATA): These are the latest generation of hard drives which will supercede IDE. Faster, with simpler cabling requirements, already in the latest desktop machines, and for around the same price as IDE, if you’re looking for performance and future-compatibility, this is the way to go. Comes in original SATA/150 and newer & faster SATA/300 flavours, with the latter being backwards-compatible.
External Interfaces:
Hard-disks themselves only come in the above three flavours, so all enclosures/boxes that you put them in will have some sort of bridge to enable you to connect them with host computers.
SCSI: As above, forget it….
USB 2.0 (480Mbps): Maximum compatibility with host computers - virtually every machine on the planet has a USB port. Even a very old machine with only USB 1.0 ports can mount a drive with a USB 2.0 interface, albeit at a painfully slow speed. Virtually the same speed as Firewire, although I prefer the latter overrall.
Firewire (400Mbps): Firewire revolutionised the storage industry with it’s simple, fast, and reliable interface. Despite being slower than USB 2.0 on paper, in practice it is sometimes faster, and I find has fewer problems because it doesn’t create any CPU load for the host computer. Multiple drives can be daisy-chained together up to 60-odd devices, so you don’t need a hub like USB 2.0. Less likely to be found on Windows machines by default however, although firewire PCI or PCMCIA cards are very cheap and easy to find these days.
Firewire 800 (800Mbps): The latest incarnation of firewire doubles the interface speed, whilst maintaining full compatibility with Firewire 400 devices. Excellent for high-speed requirements such as video work and great to have but for most archiving purposes FW400 would suffice. Found on few existing machines and doesn’t seem to be gaining much market-share e.g. the latest MacBook Pro from Apple surprisingly dropped FW800. Also note the FW800 implementation on Apple PowerMac G5s has been poor, resulting in less than the promised doubling of speed. Still a great interface though.
External SATA (eSATA): Compared to Firewire or USB, eSATA is up to six times faster and is rapidly becoming widespread as an external storage connector technology because of its excellent performance. eSATA is probably one of the reasons Firewire 800 has not gained much market-share, as eSATA looks to be the dominant technology in the future. The only downside is you’re unlikely to find it on many existing machines, and whilst eSATA cards are easy & cheap to find, if you’re looking to move the drive around between computers this may not be your best option. Fortunately there are many eSATA enclosures that also have USB/Firewire connectivity.
Ethernet (Fast ethernet - 100Mbps/Gigabit Ethernet - 1000Mbps): Drives with Ethernet interfaces (i.e. Network Attached Storage devices) are somewhat different than the above. It is better to think of them as mini-computers in themselves. A small processor inside provides simple file-sharing capabilities to/from the drive in the same way as sharing a folder or drive on your own computer over the network. Filesharing is usually via SMB/CIFS which is supported by almost all operating systems. Usually it will have some sort of web-interface to control who can access what. Gigabit is a lot faster than 100Mbps ethernet, but you need to have gigabit capability on the host computer and on your router/switch to take advantage of it. How well it performs depends a lot on how that particular company has implemented it in the box and the speed of the inbuilt processor. Also it slows down significantly when transferring large numbers of very small files, because of the TCP/IP overhead involved per file transaction, though that shouldn’t be much of a problem for image-archiving. Has the advantage of being able to be connected directly to a router/switch thus giving instant sharing amongst multiple machines on a network, without needing a dedicated computer running all the time providing file-sharing services. Cables can be very long too.
Internal vs. External?
So far we have been mainly considering external RAID boxes, but if you have a desktop machine there is no reason why you shouldn’t just drop in a PCI Raid card and some internal drives. Or even just some new drives and create a RAID-1 volume in software. I haven’t tried it on Windows but in MacOSX it is very easy indeed to set up.
Advantages of Internal systems: Cost - no need for the relatively expensive enclosure. No additional external power supply needed.
Disadvantages of Internal systems: Most desktops have limited space for drives inside. If adding more drives you need to make sure ventilation and cooling are sufficient to keep the drives from overheating, which can be a cause of early drive failure. If all of your drives are in your desktop in some ways you are putting all your eggs in one basket.
Advantages of External systems: Portability, self-contained, ability to move it between different machines. Don’t need to have the drives powered on every time you want to use your system. Can keep buying additional external boxes as your storage needs require.
Disadvantages of External Systems: Cost - whilst external boxes are increasingly cheap these days, it’s still cheaper to just put bare drives into an existing desktop.
Next page: 5. Network Attached Storage (NAS)
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