Lab test: portable hard drives

Anthony Caruana
23 April, 2011
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For the past few years the external hard drive market has been marked by little change. Although SATA has now eclipsed IDE as the interface of choice for connecting drives to computers and drive enclosures, the main feature of the storage game has been a continual plummeting of the cost per gigabyte. But a new era is dawning.

Apple has completely bypassed eSATA as a connection standard, preferring to stick to USB 2.0 and FireWire 800. However, this year we’re seeing two big changes. USB 3.0 devices are starting to come out, and solid state drives are now moving into the mainstream as prices fall.

The great promise of USB 3.0 is speed. Whereas USB 2.0 maxes out at 480Mbps, USB 3.0 can deliver 5Gbps. In order to get the benefit of the 10x speed boost you’ll need a device with a USB 3.0 host adaptor. For Mac users, that means waiting until Apple delivers new models with USB 3.0 built into the motherboard – which they may or may not do. At the time of publication, it’s widely thought that Apple may adopt Intel’s Light Peak technology instead.

However, don’t let that dissuade you from investing in the future. USB 3.0 devices plug into USB 2.0 ports and deliver full USB 2.0 performance.
The big ‘but’ here is the cables. USB 2.0 and 3.0 share the same connectors, but getting the speed boost needs a redesign of the cables. This mimics the introduction of USB 2.0 following USB 1.0.

Solid-state drives are now mainstream. Apple offers them as an option in many models and as standard in the MacBook Air. Over the last year, the price of SSDs has fallen and smaller ones can be bought for under $100.

Our suggestion is that if you need 16GB or less then a USB key will offer the best bang for buck. For up to 256GB, a portable SSD is worth considering as the drive will be under $500. At above that capacity a traditional spinning hard drive offers the best value for money.

An SSD offers benefits such as performance and power consumption. However, portable drives are typically used to move data from one place to another. That means lots of writes and deletions. Though you put a lot of files on your Mac’s internal drive, many of those are written once and rarely changed. For example, the operating system and your main apps will only change when there’s a system update.

With an external drive, you’ll typically be adding and removing files often. That’s an issue, as OS X wasn’t made with SSDs in mind.

When a file is deleted from an SSD, what actually happens is that the part of the drive with the file is marked as available but the data stays there. As the drive fills, performance slows because subsequent data writes require the old data to be deleted before new data can be written.

Newer SSDs support a command called TRIM that does this cleanup, but Snow Leopard doesn’t support TRIM. However, if you’re planning to use the external drive for iPhoto or iTunes then this might not be a significant issue.

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