How to set up external hard drive on OS X

When you first attach a new external hard drive to your Mac, it should mount and be
ready to use; however, before relying on it,
consider first taking a couple of precautionary steps to ensure that the drive continues to work as expected.

One of the first things to take into account is
that the drive is likely preformatted to FAT32
instead of a more OS-specific format. Since
FAT32 is readable and writable on both
Windows and OS X systems, this is quickest
way for a drive to work on each platform;
however, it does have some limitations,
including the lack of journaling support that
would help prevent data corruption, and lack
of support for filesystem permissions. In
addition, FAT32 drives usually come with the
Master Boot Record partition scheme, which
does not work with Apple's CoreStorage
routines, and therefore will not allow OS-
supported encryption of the drive (among
other customizations).

Sometimes drives will come with special
drive management software on them that will
give you options for partitioning the drive
and backing up your files to it. While these
may be convenient, they are not the most
recommended approach to managing the
drive. For one, unless the drive uses a
special multidisk RAID setup, OS X already
comes with all the necessary tools for
managing the drive. Additional tools from
third-party manufacturers may lead to
compatibility problems, as was recently seen
when incompatible drive management
software resulted in data loss for a number
of people who had upgraded to OS X
Mavericks.

Because of this, if the drive you have
purchased is a special RAID array, then you
may have to use the manufacturer's setup;
however, if it is a single-drive device, then
before using it be sure to format it using
Disk Utility in OS X. If the drive is going to
be used only with your Mac and with other
Macs, then consider using Apple's Mac OS X
Extended (Journaled) format, and only use
FAT32 if you intend to use the drive with a
Windows system.

To format the drive, attach it to your system
and open Disk Utility, and then perform the
following steps:

1. Select the drive device in the list of
devices, which is the item above any
storage volumes on the drive, and which
may show the manufacturer name, media
size, and so on.

2. Choose the "Partition" tab that appears.
3. Select "1 Partition" from the drop-down
menu (or more, if you have specific need
for more than one volume).

When you select a new partition layout from the drop-down menu, each new partition will be formatted to Mac OS Extended (Journaled) by default, but be sure to double-check this by selecting each in the partition diagram and then choosing the format for it.

4. Click the Options button and ensure "GUID" is selected as the partition scheme.

5. Click Apply to save the changes.
When this is done, the disk should unmount
and then remount with the new formatting
settings, and now be ready for use. Generally
a format of the drive in this manner is all
that is needed; however, some people may
wish to test drives further to make sure the
media does not contain any bad blocks or
other errors beyond the scope of the drive's
formatting.

For most in-depth testing of drives, a third-
party tool like Drive Genius or Tech Tool Pro
can be used, but Disk Utility does support
one option, which is to use the Secure Erase
option to write zeros to the disk surface. To
do this, select the volume, then click Secure
Erase in the Erase tab, and drag the Secure
Erase slider to the second position before
clicking OK. This will cause each available data block to be accessed and written to, and if one is bad then the disk will allocate a spare block in its place and ensure that the logically writable storage space is available for use. Secure Erase and other similar options that test each storage block of a device may take a number of hours to complete, but it reduces the number of potential problems with the drive.

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