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Reviving a Hard Drive for Use With Your Mac

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Reviving a Hard Drive - Erasing and Scanning for Bad Blocks
Reviving a Hard Drive - Erasing and Scanning for Bad Blocks

All drives, even brand new ones, have bad blocks. Manufacturers expect drives to not only have a few bad blocks, but to develop them over time.

Screenshot courtesy of Coyote Moon, Inc.

With the patient, er, drive hooked up to your Mac, we're ready to start the revival process.

The first step is a simple erasure of the drive. This will confirm that the drive can respond to and perform basic commands. Later, we will be performing steps that will take a great deal of time, so we want to be sure up front that it's worth spending time and trouble on the drive. Erasing the drive is an easy way to find out.

Mount the Drive

  1. Make sure the drive is powered on and connected to your Mac.

  2. Start up your Mac, if it isn't already running.

  3. One of two things should happen. The drive will appear on the Desktop, indicating that it mounted successfully, or you'll see a warning message about the drive not being recognized. If you see this warning, you can ignore it. What you don't want to want is Door #3, where the drive doesn't show up on the Desktop and you don't see any warning. If that happens, try shutting down your Mac, powering off the external drive, and then restarting in the following order.
    1. Turn the external drive on.

    2. Wait for the drive to get up to speed (wait a minute for good measure).

    3. Start up your Mac.

    4. If the drive still doesn't appear, or you don't get the warning message, there are still a few more things you can do. You can try shutting down the Mac, and changing the external drive to a different connection, using a different USB port, or changing to a different interface, such as from USB to FireWire. You can also swap out the external for a known good drive, to confirm that the external case is working correctly.

If you still have problems, then it's unlikely that the drive is a candidate for revival.

Erase the Drive

The next step assumes that the drive appeared on the Desktop or you received the warning message mentioned above.

  1. Launch Disk Utility, located at /Applications/Utilities.

  2. In Disk Utility's list of drives, locate the one you are attempting to revive. Externals usually show up last on the list of drives.

  3. Select the drive; it will have the drive size and manufacturer's name in the title.

  4. Click the Erase tab.

  5. Make sure the Format drop-down menu is set to "Mac OS Extended (Journaled)."

  6. Give the drive a name, or use the default name, which is "Untitled."

  7. Click the Erase button.

  8. You will be warned that erasing a disk deletes all partitions and data. Click Erase.

  9. If all goes well, the drive will be erased, and will appear in the Disk Utility list with a formatted partition with the name you created, above.

If you receive errors at this point, then the chances of the drive successfully completing the revival process are diminished, although not completely gone. But be aware that the next steps are very long, and drives that fail at being erased in the step above are more likely to fail in the next step as well (some will make it through and be usable).

Scanning for Bad Blocks

This next step will check every location of the drive and determine that each section can have data written to it, and the correct data read back. In the process of performing this step, the utilities we use will also mark any section that is unable to be written to or read from as a bad block. This prevents the drive from using these areas later.

All drives, even brand new ones, have bad blocks. Manufacturers expect drives to not only have a few bad blocks, but to develop them over time. They plan for this by reserving a few extra blocks of data that the drive can use, essentially swapping a known bad block of data with one of the reserved blocks. This is the process we're going to force the drive to undertake.

We're going to show you two ways to do this, using two different drive utilities. The first will be Drive Genius. We prefer Drive Genius because it's faster than the method that Apple's Disk Utility uses, but we will demonstrate both methods.

Scanning for Bad Blocks With Drive Genius

  1. Quit Disk Utility, if it's running.

  2. Launch Drive Genius, usually located at /Applications.

  3. In Drive Genius, select the Scan option.

  4. In the list of devices, select the hard drive you're attempting to revive.

  5. Place a check mark in the Spare Bad Blocks box.

  6. Click the Start button.

  7. You will see a warning that the process can cause data loss. Click the Scan button.

  8. Drive Genius will start the scan process. After a few minutes, it will provide an estimate of the time needed. In most cases, this will be anywhere from 90 minutes to 4 or 5 hours, depending on the drive size and the speed of the drive interface.

  9. When the scan is complete, Drive Genius will report how many, if any, bad blocks were found and replaced with spares.

If no bad blocks were found, the drive is ready to use.

If bad blocks were found, you may want to go on to the optional drive stress test on the next page of this guide.

Scanning for Bad Blocks with Disk Utility

  1. Launch Disk Utility, if it isn't already running.

  2. Select the drive from the list of devices. It will have the drive size and manufacturer's name in the title.

  3. Click the Erase tab.

  4. From the Format drop-down menu, select "Mac OS X Extended (Journaled)."

  5. Give the drive a name, or use the default name, which is "Untitled."

  6. Click the Security Options button.

  7. Select the option to overwrite the drive with zeros. In Lion, you do this by moving the slider from Fastest to the next indent to the right. In Snow Leopard and earlier, you do this by selecting the option for a list. Click OK.

  8. Click the Erase button.

  9. When Disk Utility uses the Zero Out Data option, it will trigger the drive's built-in Spare Bad Blocks routine as part of the erasure process. This will take quite a while; depending on the size of the drive, it can take as little as 4-5 hours or as much as 12-24 hours.

Once the erasure is complete, if Disk Utility shows no errors, the drive is ready to use. If errors occurred, you probably won't be able to use the drive. You can try repeating the entire process, but it will take a great deal of time, and the chances of success are slim.

Go on to the next page for the optional drive stress test.

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