Q We have several Macs, sharing many digital photos stored on two external hard disks, one of which seems to have failed. Although the failed drive has a ‘triple’ interface, when connected to any Mac the drive appears in System Profiler but does not mount in Disk Utility, nor on the Desktop; its blue indicator light blinks, but nothing else happens. Is there anything else I can do to recover it? Is it worth replacing the disk inside it, or would we be better with a new external drive, or even a NAS unit?

A If Disk Utility does not recognise the drive and mount it, you can try a third party utility such as Drive Genius, although you might see this as pouring good money after bad. It is possible to replace disks in such units, but seldom worthwhile. Most of the cost of the unit rests in the disk itself, as the case is fairly cheap; you would therefore do best to buy a replacement unit.

If most of your files are needed by one Mac, then you will be much better hooking up an external drive to that Mac, sharing it out to give others the access as they need. Network-attached Storage (NAS) devices can be valuable if you really need networked storage, and can accept the network overheads that they will bring. They can also be more tricky to maintain, and may have quirks or lack support for Time Machine and other Mac-specific features.

There are two strategies for buying NAS or external drives: buy cheap and expect failure in around 3 years, or invest in something more expensive with ‘enterprise’ specification disks, in the expectation of them lasting 5 years or more.

The snag with most branded units is that they tend to use regular quality hard disks, which have a marked tendency to fail soon after their warranty expires, normally 3 years. Specialist firms, such as Span, offer a range of enclosures into which you can insert disks of your choice, such as Seagate Enterprise/Constellation or Hitachi Ultrastar.

When buying multiple disks, ensure they come from different batches to avoid the risk of near-simultaneous failure; you may need to source them from different suppliers to ensure that. For external drive cases, look for a USB 3 interface; Thunderbolt would be excellent, but currently remains unusual and costly. A single drive USB 3 case will cost £20-£30, but one with Thunderbolt and USB 3 is around £170 at present.

Comments Further details of disk recovery and repair are given in this article.

Updated from the original, which was first published in MacUser volume 28 issue 05, 2012.