This page focuses on desktop, mains powered external hard disks. You can read about portable external hard drive here.
Most hard disks, whether internal, external or portable are either 3.5″ of 2.5″ – this means the diameter of the platters that hold the data are 3.5″ (87.5mm) or 2.5″ (63.5mm) diameter, though some devices use a 1″ (25.4mm) drive 3.5″ hard disks have been the standard for servers and desktop computers for many years, and 2.5″ hard disks have been the most popular size for laptops.
However enterprise class 2.5″ drives are now increasingly being used in some desktop computers and servers due to their low power uasge. With manufacturers like HP, Western Digital, Seagate and Samsing now selling 2.5″ drives with capacities up to 2tb it is probable that within a few years most magnetic hard disks are likely to be 2.5″.
External Hard Drive – Direct Attahed Storage (DAS)
An external hard drive, usually built into it’s own enclosure is the simplest and most cost effective way of keeping local, onsite backups with most manufacturers now offering these devices for under $100.
Often confusing to buyers, an External Disk is also know as Direct Attached Storage or DAS. This differs form NAS or SAN in that the device is directly attached to one computer or server. It normally remains in one place, though is easily transported.
Mains powered DAS drives are more cumbersome than USB powered portable drives but are musch less costly per MB of data capacity and usually have an inbuilt fan to keep the device cool – thus minimising errors, particularly when working hard doing a large backup. $ for $ they also tend to have a hgher capacity and faster Read / Write speeds.
Interface Data Speeds
DAS drives usually conenct via:
- USB2 – 440 Mbit/s
- USB3 – 5 Gbit/s
- eSata – 6 Gbit/s
- Firewire 400 -400 Mbit/s (used on some MAC computers)
- Firewire 800 -800 Mbit/s (used on some MAC computers)
- Thunderbolt – 10 Gbit/s
Don’t be blinded by these numbers. They are theoretical maximum, and not attained in normal use.
The other consideration is that your typical magnetic hard drive can only read and write data at around 150 – 200 mb/s
So unless you are using a Solid State Disk anything other than USB 2 will be sufficient for your needs.
One small advantage with eSata is if your computer has an eSATAp interface you can directly connect a bare hard disk (ie you do not need a full DAS enclosure or USB power source. The disadvantage with this as a day to day backup is the much bigger chance of damaging the cable, the interface or the drive – as you are very likley to let it fall of a desk.
External Drive for media files
A popular use for DAS is for video editing. Rather than slow down a whole network or fill the main server drive, individual users can keep their media files on an external drive connected directly to their personal computer. This minimises load on the network and allows the user to easily move the device to another computer – in the same building or elsewhere, possibly home.
One major drawback with this working practice is that you can be very sure that most users will not have up to date backups of those valuable files.
External Drive – Storage vs Backup
You need to be sure you know the difference between Backup and Storage before using DAS.
is the location your main files are located. Usually on the hard disk in your Desktop, Laptop or Server, however many individuals or organisations allow their main storage for some files to be on some form of protable device (see media files above). How many people walk about with a USB flash drive as the only location for critical data?
is the location where you keep a copy of your data on different media, a different device or possibly online. ou work on your files read & write) to the normal storage location and make pereodiv backups to the backup device or location.
As suggested with using DAS for media files it is a very weak strategy to have the only copy of any files (storage) on a single hard disk -particularly when it is not saftely located inside your computer housing ie your main Hard Disk.
Common causes of data loss on External Drives:
- Theft – easy to walk out of an office with the complete enclosure
Physical damage – easy to knock it off a desk on to the floor.
Liquid damage – less likley but open to the office environment, so a cup of coffee could be spiled over it.
If you are using an extenal drive for any of your main data storage (because it is cheaper than a dedicated media server or you want the portability convenience), then you really need to include that drive in your system automatic backup process.
Direct Attached Storage is really best suited as a location to backup data, usually from a single desktop, laptop or server. It is the most cost effective and fastest method of backing up data. However unless you are under a really tight budget it is not the most resilient backup method.
For more reselient backup methods look at also including at lease one of the following:
- (offsite) Online / Cloud backup
NAS Backup / Backup Appliance