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Archived - Troubleshooting Hard Drives: Reformatting in Mac OS 8 and Mac OS 9

This article discusses when to reformat the hard drive of a Macintosh computer, with a focus upon repairing damage to the disk's formatting structure using Apple's disk utilities. An introduction to the terminology is provided.

This article has been archived and is no longer updated by Apple.

TROUBLESHOOTING PATHS

    The following two troubleshooting paths address the problem of formatting structure damage, the cause of most unplanned disk reformatting. Using Apple's disk utilities, one path addresses damage to the logical formatting structure, the other to the physical formatting structure. Both lead toward reformatting the disk, but are organized to avoid it when possible.

    The "Terminology" section and onward briefly introduces the concepts but is not prerequisite to using these paths.

    Symptoms

    Formatting structure damage may result in read/write errors, missing files, and files that cannot be opened, moved, copied, or deleted. Damage to the data stored upon the drive may also result, such that almost any software problem or Mac OS error message could indirectly signify formatting structure damage. Though the -127 error is a more familiar indicator than some others, the problem must be confirmed through the use of the proper disk utility whenever damage is suspected.

    When to Use the Paths

    - Path to a High-level Format: Use at any time when troubleshooting for the symptoms described, but before performing time-consuming tasks like clean-installing the operating system.

    - Path to a Low-level Format: Use whenever symptoms suggest that the other path may have failed to resolve the problem, or when using the disk testing function of Apple's formatting utilities: Drive Setup, Apple HD SC Setup, or Internal HD Format.


The Path to a High-level Format
(Fixing logical formatting structure damage)

1. Start up the computer from a disk other than the one to be repaired.

If you are pressing Command-Option-Shift-Delete during startup, release the keys as soon as the startup screen appears or the hard disk may not mount. Note: This key sequence does not work with all Macintosh models and is not supported. Pressing the "c" key during startup is another method.

2. Open Disk First Aid from a disk other than the one to be repaired.

3. Does the volume to be repaired appear in the Disk First Aid window?

    YES: Continue to the next step.
    NO: Quit Disk First Aid. Go to step 7.


4. In the Disk First Aid window, select the volume to be repaired, then start the Repair function. Wait for it to complete. Does Disk First Aid report that the volume appears to be OK or that it was repaired successfully?

    YES: Stop. Do not format. The logical formatting structure is undamaged. To confirm the result, this step may be repeated.
    NO: Repeat this step once. If the answer is the same, continue to the next step.


5. Does Disk First Aid report that problems were found but it cannot repair them?

    YES: Quit Disk First Aid. Go to step 8.
    NO: Continue to the next step.


6. Disk First Aid reports that it cannot start or continue the repair because of some other problem.

    If the nature of the problem is not made clear, consider the following: Disk First Aid will not repair a disk that is write-protected, is not an HFS disk, has applications currently open, has a damaged hard disk driver, is being shared, or is being used for virtual memory. If all else fails, quit Disk First Aid and go to step 8.


7. Shut down the computer and disconnect all external devices except the keyboard, mouse, and monitor. If the disk to be repaired is among them, leave only it connected.

Start up the computer from a system disk and open Drive Setup, Apple HD SC Setup, or Internal HD Format (the "Utilities" section of this article explains which to use).

Does the disk to be repaired appear in the disk utility's window?

    YES: Continue to the next step.
    NO: Stop. There may be a hardware problem. NOTE: Internal HD Format may not locate the disk if it is using a hard disk driver installed by another utility, including Drive Setup. If there is any doubt, use Drive Setup instead.


8. If you are arriving at this step for the second time, go to step 11 now.

Open Drive Setup or Apple HD SC Setup (the "Utilities" section of this article explains which to use). Internal HD Format cannot be used in this step because it has no separate option to install the hard disk driver. If possible, use Drive Setup; otherwise, go to step 11 now.

Is the button or the menu command to "update" the driver dimmed?

    YES: Go to step 10.
    NO: Continue to the next step.


9. Update the hard disk driver. Did the driver install successfully?

    YES: Quit the disk utility, shut down the computer, and return to step 1.
    NO: Go to step 12.


10. The version of the hard disk driver already installed may be newer than what the disk utility installs. The most current version of each Apple utility can be downloaded from Apple Software Updates. If you are using Internal HD Format, download Drive Setup instead. If there is no newer disk utility, go to step 12 now.

If a third-party hard disk driver is installed, it should be updated with the utility that installed it. Refer to Knowledge Base article 24585: "Hard Disk Driver: Identifying It And Ensuring Compatibility."

Use the newer disk utility to try updating the driver again. Could the driver be installed?

    YES: Quit the disk utility, shut down the computer, and return to step 1.
    NO: Go to step 12.


11. Try using a newer version of Disk First Aid, if available. The most current version of Disk First Aid can be downloaded from Apple Software Updates. If there is no newer version, either continue to the next step now, or try using a different disk repair utility. A list of commercial disk utilities is available at the bottom of this article.

Will you try a different disk utility or a newer version of Disk First Aid?

    YES: Return to step 1 and use the new Disk First Aid. If using a third-party disk utility, proceed according to the requirements of that utility.
    NO: Continue to the next step.


12. Initialize the disk using the appropriate Apple formatting utility. If using Drive Setup, do not configure it for a low-level format (a high-level format is the standard setting).

CAUTION: Formatting a disk permanently erases all information from it. If possible, copy important files to another disk first.

If a third-party hard disk driver is installed, Apple's formatting utilities may not be able to format the disk, though newer versions may work. Use a third-party disk utility if necessary. Refer to Knowledge Base article 24585: "Hard Disk Driver: Identifying It And Ensuring Compatibility."

13. Did the format complete successfully?

    YES: Stop. The logical formatting structure has been recreated is no longer damaged.
    NO: Continue to the next step.


14. Was the unsuccessful format performed by Apple HD SC Setup or Internal HD Format?

    YES: Try formatting the disk again. If still unsuccessful, stop. There may be a hardware problem.
    NO: Continue to the next step.


15. Was the unsuccessful format performed by Drive Setup or by another utility configured to perform a high-level format? (A high-level format usually takes less than a minute to complete; a low-level format takes much longer.

    YES: Go to the next section, "The Path to a Low-level Format."
    NO: Stop. There may be a hardware problem.



The Path to a Low-level Format
(Fixing physical formatting structure damage)
Note: For information on why a low-level format may not be an option, see technical document 24764 "Drive Setup: Checking For Bad Blocks"

1. Follow the steps provided in "The Path to a High-level Format" until instructed to stop. Note that neither path will fix a hardware problem.


2. Start up the computer from a disk other than the one to be repaired.

3. Was the disk just formatted by Apple HD SC Setup, Internal HD Format, or another utility configured to perform a low-level format? (A high-level format usually takes less than a minute to complete; a low-level format takes much longer.)

    YES: Stop. The successful low-level format just performed confirms that the physical formatting structure is undamaged.
    NO: Continue to the next step.


4. Is this a PCI-based computer? (PCI-based computers include the PowerBook 3400 and all PowerBook G3's and later, plus all Power Macintosh computers other than the 6100, 7100, and 8100 series.)

    YES: Continue to the next step.
    NO: Go to step 8.


5. Open the System Folder of the current startup disk (not the disk to be repaired), then open the Extensions folder inside. Is the Insomnia extension present?

    YES: Go to step 8.
    NO: Continue to the next step.




    Figure 1: Insomnia


6. Open the Apple menu and select Control Panels. Is Energy Saver among the Control Panels, and can it be opened successfully?

    YES: In the Energy Saver window, click "Show Details," then set each control to "Never." Close the control panel and go to step 8.
    NO: Continue to the next step.


7. PCI-based Macintosh computers may go to sleep during a disk test if left unattended for longer than 30 minutes, causing the test to fail. Choose one of the following preventive measures before continuing to the next step.

    1. During the disk test, do not allow more than 30 minutes to pass without resetting the sleep timer, which can be accomplished by a movement of the mouse.
    2. Create a startup disk that includes both the Energy Saver control panel and the Energy Saver extension, placed into their respective places in the System Folder. After starting up from that disk, open the Energy Saver control panel and set each control to "Never."
    3. Create a startup disk that contains the Insomnia extension in the Extensions folder. This extension can be obtained from the System Folder of system CD's that include it.


8. Open the appropriate Apple formatting utility from a disk other than the one to be repaired, then start the "Test Disk," "Test," or "Scan For Defects" function, depending upon the utility. The test may take as long as an hour or more to complete, depending upon the disk.

Did the disk utility report that no errors were found, or that they were corrected or recovered?

    YES: Stop. Do not format. The physical formatting structure is undamaged.
    NO: Continue to the next step.


9. Before low-level formatting, it is best to isolate the computer from external devices first, as they may prevent it from completing successfully. Shut down the computer and disconnect all external devices except the keyboard, mouse, and monitor. If the disk to be formatted is among them, leave only it connected.

10. Low-level format the disk. Apple HD SC Setup and Internal HD Format always perform low-level formats, but Drive Setup will not unless first configured to do so: select "Initialization options" from the Functions menu, then click "Low-level format."

CAUTION: Formatting a disk permanently erases all information from it. If possible, copy important files to another disk first.

If a third-party hard disk driver is installed, Apple's formatting utilities may not be able to format the disk, though newer versions may work. Use a third-party utility if necessary. The Knowledge Base contains information about how to identify hard disk drivers .

Did the format complete successfully?

    YES: Stop. The physical formatting structure has been recreated and is no longer damaged.
    NO: Stop. There may be a hardware problem.



TERMINOLOGY

LOW-LEVEL FORMAT

    A low-level format creates the physical formatting structure of the hard disk, recording the magnetic markers that divide the total usable space into sectors and tracks, thus providing the foundation upon which a high-level format builds the logical formatting structure. Drives sold to consumers today come low-level formatted, and many come high-level formatted for either the Mac OS or other operating systems.

    Because it recreates the physical formatting structure, low-level formatting may repair damage to it that cannot be repaired by sector sparing with Drive Setup or other utilities, but erases the disk in the process.

    Low-level formatting requires much more time to complete than a high-level format. Smaller disks require at least several minutes; larger disks as much as an hour or two or more.

    Note: For information on why a low-level format may not be an option, see technical document 24764 "Drive Setup: Checking For Bad Blocks"



HIGH-LEVEL FORMAT

    A high-level format creates the logical formatting structure of the hard disk, comprised of data structures such as the boot blocks, volume information blocks, volume bitmap, extents tree, catalog tree, and data tree--structures that are often collectively called the directory structure and which have to do with maintaining information about the disk and the location of data stored upon it.

    These structures support the HFS (hierarchical file system) volume that is created in the process, represented by the disk's icon on the desktop. A high-level format thus completes the process of preparing the disk to receive the operating system and any user data. A disk driver is also written, handling write and read functions to and from the hard disk.

    Because it recreates the logical formatting structure, high-level formatting repairs damage that cannot be repaired by Disk First Aid or other such utilities, but erases the disk in the process. It does not verify or repair physical formatting structure problems.

    High-level formatting typically requires less than a minute to complete, and often only a few seconds.


INITIALIZATION

    Initialization refers to the process of preparing a disk for use by the Macintosh operating system via formatting. It is commonly used to refer to a high-level format alone, though the term is not specific to either type of format.


SECTOR SPARING

    Damage to the physical formatting structure means bad sectors--blocks of the disk that can no longer be written to or read from successfully because the magnetic markers that define them have either been removed or altered. Depending upon the kind of damage and where it is located, a low-level format can either repair the affected sectors by recreating those markers, or work around them by sector sparing, also known as block reallocation: recoverable data is moved to good blocks, and the bad block is rendered unavailable for the disk driver to write to in the future.

    Sector sparing can also be performed by the Test Disk function of Drive Setup and other Apple formatting utilities, which scans a disk for bad sectors by checking the integrity of blocks of data read from and copied back to the disk. This function takes about as long to complete as a low-level format, but has the key benefit of not erasing the disk in the process.

    Because the Test Disk function does not perform low-level formatting, some bad sectors that might have been repaired by doing so will only be spared. However, this difference is rarely significant enough to warrant low-level formatting except where Test Disk fails a disk or recommends it be low-level formatted.

 




UTILITIES

    Drive Setup, Apple's current formatting utility, is for use with SCSI and IDE/ATA hard drives in Macintosh computers with Power PC or '040 processors. Drive Setup performs a high-level format by default, but will low-level format first if configured to do so. Of the Apple disk utilities, only Drive Setup can perform a high-level format separately from a low-level format. Drive Setup can verify and repair the physical formatting structure of a hard disk without reformatting.
    Note: For information on why a low-level format may not be an option, see technical document 24764 "Drive Setup: Checking For Bad Blocks"

 


    Apple HD SC Setup is for use with SCSI hard drives in 68K Macintosh computers (non-Power Macintosh computers). Apple HD SC Setup always performs a low-level format followed by a high-level format. Apple HD SC Setup can verify and repair the physical formatting structure of a hard disk without reformatting.

    Internal HD Format, now obsolete, was Apple's formatting utility for IDE hard drives before support for those drives was brought to Drive Setup. Use of Drive Setup is preferred. Internal HD Format always performs a low-level format followed by a high-level format. Unlike the other two utilities, it does not provide a separate option for installing the hard disk driver alone. Internal HD Format can verify and repair the physical formatting structure without reformatting.

    Disk First Aid is Apple's utility for verifying and repairing the logical formatting structure of Macintosh volumes. It cannot create, verify, or repair the physical formatting structure of a disk, nor can it high-level or low-level format any disk.



OVERVIEW: WHEN TO HIGH-LEVEL FORMAT A HARD DISK

  • When the logical formatting structure of the disk has become damaged and cannot be fixed by Disk First Aid or other compatible disk utilities.
  • When, even after attempting to reinstall the hard disk driver, the disk fails to mount or cannot be read by Disk First Aid, but is still available to the formatting utility.
  • When partitioning the disk. For more information about partitioning, see the online Drive Setup Guide included with the utility.
  • When optimizing the disk. Optimizing is also known as defragmenting. For more information, see article 17933: "Macintosh: How Often Should I Defragment My Hard Drive?". There are third-party utilities that can optimize without formatting, but it is no less important to back up important data first.
  • When converting a volume's HFS format from HFS Standard to HFS Extended, or vice versa. For more information, see article 30344: "Mac OS 8.1: About Mac OS 8.1 Extended Format"
  • Sometimes, when replacing an existing hard disk driver with one of different make or one of the same make but of sufficiently different version. For example, Drive Setup requires a high-level format to install its driver over one installed by a third-party utility.


OVERVIEW: WHEN TO LOW-LEVEL FORMAT A HARD DISK

- When the physical formatting structure of the disk has become damaged and cannot be repaired by sector sparing with a compatible disk utility.
- When, even after several attempts, a high-level initialization fails to complete successfully.


FREQUENTLY ASKED QUESTIONS

What causes formatting structure damage?

    Logical formatting structure damage can occur when something interferes with the normal, ongoing updates that are written to its various data structures, such as the catalog tree or extents tree. Causes include:

    - Software-related crashes or conflicts due to corrupt or incompatible applications, extensions, and system software.
    - Incompatible hard disk drivers.
    - Malicious applications like viruses.
    - Not restarting or shutting down the computer properly.
    - Hardware-related crashes or interference due to a variety of possible issues with internal or external devices and their cabling, termination, or firmware.
    - Problems with RAM and other expansion hardware.
    - Electromagnetic interference (EMI) and power fluctuations (brownouts and overvoltages).
    - A damaged physical formatting structure.

    Physical formatting structure damage can be caused by some of the same things that cause logical formatting structure damage and by areas of real damage to the surface of the disk itself, like scratches or pits; also by degradation or contamination of the disk surface or drive heads due to smoke, dust, or particles of the disk media itself.


Why would a format fail?

    A low-level format will fail when the maximum allowable number of bad blocks has been exceeded on the disk as a whole or in certain key areas. Because hardware and software interference can contribute to errors when writing to or reading from the disk, isolating the computer from unnecessary internal and external hardware, and starting up from a known-good system disk may permit a format that might otherwise fail.

    A high-level format will fail when the formatting utility is unable to successfully write the logical formatting structure to the hard disk, often due to bad sectors. In that event, low-level format or use a disk utility to spare bad sectors before attempting another high-level format.


After repairing the formatting structure, is the data on the disk still good?

    Damage to data stored on the disk, including the operating system, may have occurred if there are continuing problems not related to hardware issues or software incompatibilities. Though damaged applications will need to be reinstalled, some third-party utilities do allow at least partial recovery of files that are still usable in that form, such as documents, and may also recover erased files, unless the disk has been reformatted.


What if Disk First Aid and another disk utility disagree?

    If each utility is up-to-date and believed to be compatible, there is no easy of way to know which is correct. For damage that cannot be repaired by a disk utility, regardless of which utility, the user will have to either accept the potential risk to their data posed by not fixing a possible problem, or err on the side of safety and reformat.


When do I "Zero all data"?

    Many formatting utilities provide this option (also known as zeroing-out) as a security measure to ensure against the possibility that usable traces of data could be retrieved from the formatted disk. This feature will replace all the information on the disk with zeros, significantly increasing the time it takes to complete the format.
    To zero-out is not to format, so it should only be used as a security measure, not to provide for a better or more thorough format.

    Zeroing-out is not to be confused with "disk zeroing," a phrase sometimes used to refer to the process of creating the master directory block, volume bitmap, and catalog file.


If a low-level format repairs damage that a high-level format cannot, and may also repair some damage that sector sparing cannot, and if a high-level format is quickly and automatically performed after the low-level format anyway, why ever perform anything but a low-level format?

Because low-level formatting:

    - Permanently erases all data from the disk.
    - Can take a long time to complete.
    - Removes information, such as the computer's serial number, that may be recorded in an otherwise protected area of the disk. Not all Macintosh computers have this sort of information recorded onto their stock hard drives, but many do. The serial number of an iMac, for example, can be conveniently viewed in Apple System Profiler 2.x, but only if the hard drive that contains it has never been low-level formatted. The part number of the software bundle it shipped with is also provided.



THIRD-PARTY SOFTWARE ALTERNATIVES

CAUTION: Before using any third-party disk utility, ensure first that it is compatible with the computer, the version of the Macintosh operating system, and the HFS format in use.

Alternatives To Disk First Aid

Disk First Aid is entirely capable of diagnosing logical formatting structure problems on Macintosh-formatted volumes. Alternative utilities may be used in circumstances where a "second opinion" is desired, and may provide other useful functions beyond those necessary to diagnose the formatting structure, such as disk optimization, erased file recovery, and hardware diagnostics. What follows may not be a comprehensive list.


    MacMedic, by Total Recall Software
    Norton Utilities, by Symantec Corp.
    TechTool Pro, by Micromat Computer Systems

Additional Information

For additional information, please reference the following related article(s):

  2686 Macintosh: List of Disk Recovery Tools
Important: Information about products not manufactured by Apple is provided for information purposes only and does not constitute Apple’s recommendation or endorsement. Please contact the vendor for additional information.
Last Modified: Sep 22, 2009
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