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Mac OS X Disk Utility

Mac OS X provides a very useful application called Disk Utility to users. With it, you can check the status of ("verify") your hard drive, repair problems in your hard drive, burn CDs and DVDs (including multi-session disks), and create "disk images" to back up your files.

To open Disk Utility, go to Applications, then to Utilities. Double click on Disk Utility.

Disk Utility

How to Read the Information about your Disk

Disk Utility can provide both basic and more complex diagnostic information about your computer, depending on your needs. To get info on your disk, you will first need to choose either the hard drive itself or one of its partitions. Most Macintosh users only have one partition on their drive.

Drives

When you select your partition, you will see information at the bottom of your screen about the capacity of the disk, the numbers and size of files and folders, and amount of space left to you.

Mac HD

When you select your drive, you will see information on the capacity of the drive, the write status, how it is partitioned, and the SMART status. Your SMART status indicates how close the hard disk is to failing-- if it reads "About to Fail" in red, you should immediately begin backing up your data and look for a replacement drive. If your SMART status is "Verified", your hard disk is in good condition.

Hard disk

By choosing Info from the row of buttons at the top of the main Disk Utility screen, you can see some additional information on your disk and its partitions. This is most useful in checking whether your partition can be verified or repaired.

Info

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How to Verify a Disk or Permissions

Verifying is a way of testing whether your disk is in good condition. You can also verify your permissions, which determine how much control you have over files and applications on your computer. If your computer is working more slowly than usual, or has frequent errors, verifying your disk and permissions is a good place to start troubleshooting.

Verifying a Disk

  1. Select your hard drive in order to verify all of your partitions; otherwise, select only the partition you wish to verify.
  2. Choose the First Aid tab at the left top of the main window.
  3. Click the Verify Disk button. Disk Utility will begin to check the status of your disk--this may take a few minutes.
  4. If Disk Utility discovers any errors, you may wish to repair your disk. If not, your disk is probably in good condition.
Repair

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Verifying Permissions

  1. Select your hard drive.
  2. Choose the First Aid tab at the left top of the main window.
  3. Click the Verify Permissions button. Disk Utility will begin to check for permissions errors, which may take a few minutes.
  4. If Disk Utility discovers any errors or 'differences', you should repair your permissions. If not, your permissions are in good order.
Permissions

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How to Repair a Disk or Permissions

If you see any errors while verifying your disk or permissions, it is a good idea to repair them as soon as possible. Disk Utility can solve most common problems your hard drive will encounter, but it may be necessary to boot your computer from the operating system CD in order to repair its hard drive.

Repairing a Disk

  1. If the Repair Disk button is greyed out, then you will need to restart your computer from the operating system install disc in order to repair your disk. Be sure to back up your files before beginning.
    • To start your computer from your Install disc insert it and restart while holding the C key. Select the "Install Mac OS X disc" when the choice appears.
  2. Choose the First Aid tab and click Repair Disk.
  3. Disk Utility will begin to repair your disk. This may take some time.
  4. If Disk Utility reports "The underlying task reported failure", it is unable to fix whatever is wrong with your disk. You should back up your files and reinstall OS X.

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Repairing Permissions

  1. Choose the First Aid tab and click Repair Permissions.
  2. Disk Utility will begin to repair your permissions. This will take a few minutes.
  3. When it finishes, it should report that "The privileges have been verified or repaired on the selected volume".

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Creating a Disk Image

Disk Images are a useful way of organizing data, whether for further use, backup, or burning to a CD. While they are technically files with the extension .dmg, they can contain other files and folders, which makes them very useful for transporting data in situations where a folder wouldn't be convenient.

When making a new disk image, you have several options. You can choose to make a copy of an existing disk, a copy of an existing folder, or a blank disk image.

Making a Disk Image Copy of an Existing Disk

Copying an existing disk (such as your hard drive or a CD) into a disk image is most useful when you want to make a backup of a large hierarchy of files and folders. Unfortunately, you cannot back up your startup disk (usually your main hard drive) unless you've booted up from another disk, such as your Mac OS X Install Disc.

  1. Select the disk you wish to copy in the list on the left-hand side of the main Disk Utility window.
  2. Click the New Image button, and name your disk.
  3. Select read/write disk image in the Format menu bar.
  4. You can choose to encrypt your disk image with a password by selecting AES-128 (recommended) from the Encryption menu.
  5. Click Save and wait. Depending on the size of the disk you're copying, this could take some time.
  6. When it finishes, you will have a file with the name you selected and the suffix .dmg (e.g. yourfile.dmg). To access its contents, double click on the file--the disk image will "mount" and appear on your hard drive as another disk.
From a Disk

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Making a Disk Image Copy of a Folder

Copying an existing folder as a disk image is an easy way to get a large number of files onto a disk image of precise size.

  1. Choose an existing folder to copy, or create a new folder containing the files you wish to copy.
  2. In Disk Utility, choose File > New > Disk Image from Folder....
  3. Browse to the folder you plan to copy, and click Image.
  4. In Save As:, choose a name for your disk image. In Where:, choose where to save your disk image.
  5. You have several choices of format for your disk image:
    • Read-Only: after the image is created, you will not be able to add files to it, only to open or copy them. This image will be the same size as the folder you are copying.
    • Compressed: compressed images function like read-only images, but are smaller in size because of their compression. If your compressed disk image is corrupted, you will not be able to recover any of the data on it.
    • Read/Write: these disk images can have files added or removed after their creation, although their capacity will be determined by the size of the initial folder they copy.
    • DVD/CD Master: this format is used to make copies of audio and video discs. Choose this option only if you have selected a CD or DVD as the "folder" you are copying.
  6. You can choose to encrypt your disk image with a password by selecting AES-128 (recommended) from the Encryption menu.
  7. Click Save and wait. Depending on the size of the folder you're copying, this could take some time.
  8. When it finishes, you will have a file with the name you selected and the suffix .dmg (e.g. yourfile.dmg). To access its contents, double click on the file--the disk image will "mount" and appear on your hard drive as another disk.
  9. If you made this disk image to burn to a multisession disc, continue on to the Burning a Multisession Disc directions.
From a Folder

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Making a Blank Disk Image

Blank disk images are most useful when you want a disk-like storage space for files, but haven't yet decided which you need to copy-- particularly if you plan to later burn the disk image to a CD or DVD. Blank disk images can be made in any size, and "ejected" when not in use, like all disk images.

  1. In Disk Utility, choose File > New > Blank Disk Image.... Enter a name for your disk in the Save As: box.
  2. Choose where you want to save your file, and select a size for it from the Size: menu. Note that some of the available sizes are set to standard CD and DVD sizes; choosing them is an easy way to make sure you don't add too many files to your disk image later if you plan to burn it.
  3. You can choose to encrypt your disk image with a password by selecting AES-128 (recommended) from the Encryption menu.
  4. Select read/write disk image and click Create.
  5. Depending on the size of your disk image, this could take a moment. When the disk image has been created, double click your .dmg file to mount it on your hard drive. From there, you can drag files to the image to add them.
Blank Disk Image

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How to Burn a CD or DVD

"Burning" is the process of saving information to a CD or DVD. CUS has detailed directions for most methods of burning discs at the Burn a CD page. Two more advanced methods are explained below.

Burning a CD or DVD Using a Disk Image

If you've already prepared a disk image that you want burnt to a CD or DVD, burning a disc from it is very easy. Begin by Creating a Disk Image (and adding files, if you choose to make a blank disk image). Then..

  1. Select the .dmg file you wish to burn from the list on the left-hand side of the main Disk Utility screen.
  2. Click the Burn button at the upper left. If you have already inserted your blank disc, click Burn again. If not, insert the disc now and follow the instructions presented on the screen.
  3. Your disc will begin to burn. Depending on the size of the image you are burning, this could take some time.
Burning

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Burning a Multisession Disc

Multisession discs are discs that have been burnt in multiple steps, rather than all at one time. While this can be an extremely useful process, it is also somewhat more complex than burning a CD or DVD in a single session.

Important: Multisession discs will not work on any Windows computers. Use this method only if you plan to run your discs solely on Macintosh computers.

  1. Put all the items you want to burn into a folder.
  2. Launch Disk Utility (from /Applications/Utilities).
  3. From the Images menu, choose New > Image from Folder...
from folder

  1. Wait until the program is done making the image.
  2. Click Burn (on the toolbar).
  3. Click the blue triangle in the upper right to show the burn options.
  4. Make sure you select Leave disc appendable
burning in disk utility

  1. Click the Burn button and the session will be burned.
  2. Repeat this process to burn a new session on the same CD.

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