Pubblog, the makers of MailSteward and FileMyFiles, have released DiskRefresher (, an utility for refreshing the data on your external disk drives. It requires Mac OS X 10.6 or later, costs US$5.99 and is available in the Mac App Store in the Utilities category.

Hard disk drives are designed to be used regularly, not stored on a shelf for months or years. The magnetic strength of the digital bits recorded on a drive slowly decays when that drive is disconnected from a computer. DiskRefresher makes this time-consuming process simple and safe, according to the folks at Pubblog.

Manufacturers include firmware in their drive mechanisms that counteracts this inevitable bit decay. Every time a bit is accessed, the drive “refreshes” its magnetic imprint on the disk. When a drive is active and connected for an extended time, this refresh cycle runs automatically. But when a drive that has long been powered down is briefly reactivated– to copy a file or run a simple integrity scan, for instance — most bits remain unread and unrefreshed.
At launch, DiskRefresher lists the external storage drives you have mounted and shows each drive’s storage capacity. You can select one or several drives to be refreshed and you can drag a drive up or down in the queue window to adjust the refresh order.

When you click Refresh, DiskRefresher begins reading every bit on each of the selected drives. Generally, this process takes more than an hour — several hours if your drives are over 250GB. A progress bar displays the estimated time remaining in the process. No data is written to the refreshed disk.

DiskRefresher won’t alter or add any files to the disk being refreshed. It is strictly read-only. It will not attempt to repair corrupted data nor will it defragment files. To help you keep track of refresh sessions, DiskRefresher keeps a log file (in the Application Support library on your internal boot drive) that lists the drive name and refresh date. You can access this log in the menu at File > DiskRefresher History.