HOWTO MANAGE AND PROTECT DISKS
Run a health check
Select either a disk or a volume on the left, click First Aid in the toolbar and then click Run when asked to confirm the operation. Disk Utility will run through some health checks to ensure that everything is okay with the item you selected, and it will attempt to repair problems.
Format a disk for Mac
When you buy storage, it’s likely to be formatted for use with Windows. On the left, select the disk or the volume on it, then click Erase. Set Format to ‘OS X Extended (Journaled)’. (If you selected the disk, set Scheme to GUID if you want to install a second copy of OS X on it.)
Format as encrypted
Particularly with a portable drive, you might want to encrypt its contents in case you lose it. In this case, choose ‘OS X Extended (Journaled, Encrypted)’ as the format. You’ll be asked to set a password, which will be required to access the drive upon connecting it to a Mac.
Format for Windows
To share a disk with a Windows PC, set its format to ‘MS-DOS (FAT)’ if the disk or volume is under 32GB in size, or ExFAT if it’s larger than that. Its label can be 11 characters long, but filenames can be longer. Both OS X and Windows will be able to write to the disk.
Encrypt without erasing
A Mac volume can be encrypted without erasing its contents – but back them up first! In Finder, select Go > Computer, hold and click the volume, choose ‘Encrypt…’ and set a password and a reminder. After clicking Encrypt Disk, click the volume to check progress.
Partition a disk
To split a drive into smaller partitions – perhaps to limit space that’s available to Time Machine – select it (not a volume on it) and click Partition. When you click the + below the pie chart, space will be reapportioned from the volume that’s selected (shown in blue).
Back up to a disk image
You can make a disk image from a folder (useful for archiving projects). Choose File > New Image > Image from Folder, and then select a folder and click Open. The image’s contents can be compressed and encrypted. To restore an image, choose Edit > Restore.
Securely erase a disk
Some researchers say it’s unnecessary to erase a modern hard disk multiple times before it’s abandoned. If doing so eases your nerves, erase the disk to contain one partition, select that partition, click Erase, then Security Options and choose a number of passes to make.