Most people do not back up their data as rigorously as they should. Backing up data is annoying, time consuming, boring and easy to forget. Some people use an external hard drive and copy things there haphazardly. Others are more systematic. However, if you only use one external hard drive for your backups (or for transporting data between computers), that hard drive can fail. Few things are quite as terrifying as "Windows Was Unable To Access…" error messages on your only copy of data files.
Try plugging the external hard drive in with a different cable; wipe down both ends of the cable you're using and the ports it goes into with a cotton swab with a little bit of isopropyl alcohol. While it's not common, sometimes the failure to read a hard drive can be as simple as oxidation on the contacts on the cable between the two devices.
Understand how hard drives fail. Most hard drives fail because one or more sectors on the disk become unreadable – the magnetic medium that records "0" or "1" loses its magnetic potential, or gathers a spec of dust, and the read/write head on the drive mechanism can't access it. Sectors are very low-level hard drive data; files and clusters are managed at the operating system level. Avoid any backup and restore utility that doesn't give you the option to skip bad clusters. Note that Microsoft Windows backup utility lacks this option.
Use the backup software that comes with your operating system. Windows backup utility will run in the background and automatically try to copy data that's been designated for backups on a regular basis. It has some limitations – it will not skip over bad sectors on the drive to which it's copying. There are two broad categories of backup utilities. One takes a snapshot of the entire disk – called a disk image – and copies it to a fresh drive. This kind of utility is faster than a file-by-file backup system, but doesn't check the integrity of individual files. If the files you're backing up are also corrupted, you'll still have unrecoverable data.
Use third-party backup software; there may be a backup utility built into the firmware of your external hard drive. If you can access the files on the hard drive at all, copy them to a fresh drive, then try to take a fresh disk image. If you cannot access the drive at all, download a disk imaging program like Ghost, duplicate the drive to a fresh drive and try accessing that. A files-based backup will have fewer risks of things going wrong and should be tried first.
Set a habit of using two or more external hard drives and doing weekly backups, swapping out which hard drive you back up to each week. If this data is critical to your business, seriously consider storing the alternate drive in an off-site location, such as in the trunk of your car – bring in the hard drive every Friday, swap it with the one that was used to do the backup last week and set the backup utility to copy the files. Note that you should prioritize backing up your data over your applications. You already have installation media for your applications and, while it's annoying to have to reinstall the programs, with the Windows Registry, you'll have to reinstall them anyway and backing them up means more reads and writes to your external hard drives, forcing them to wear out faster.
Take your drive to a data recovery service. These companies have specialists who can disassemble the drive and attempt to read individual platters with specialized equipment. They are not cheap, but for business-critical or important family data, they can be the only thing standing between you and a total loss.
- You should also get in the habit of backing up data to a server-based backup solution. This can be as informal as copying important files to Google Drive or Dropbox or Microsoft's Skydrive, to renting server space from Amazon or a dedicated backup service like Mozy.
- Rubbing alcohol
- Cotton swab
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