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Bad HFS+ File System?
Know your disk repair tools...
There are a number of utilities available to evaluate (or verify) and repair OS X file systems. Disk tools can be categorized into three groups: built-in tools, power-tools and search-and-rescue tools.
OS X: Built-in tools
(ordered from most to least commonly used)
OS X's Disk Utility evaluates the health of the file system by comparing the structures on the disk and making sure the various components agree as to what files are present and how large they are, etc.
OS X's Disk Utility
A command line equivalent of OS X's native Disk Utility is run at system startup and it should also be automatically executed when writeable media is inserted. IF Disk Utility detects unusual disk conditions, it may determine that it should not repair the System's Boot Partition at startup. When this occurs the System will stop at a command line prompt during the boot process and instruct you what commands should be run. If you have an OS X 10.2 system or later, instead of using the command line to do this you may reboot the system in 'safe' mode.
Upon booting, when Disk Utility does not fix anything, or successfully fixed your file system - you will never realize it. Once the system has booted to the Login Screen, odds are your computer does not have a corrupted file system. Further problems from this point may reflect the presence of a preferences (.plist) file. IF you have multiple volumes, another possibility is that one or more system files has been corrupted or is missing.
OS X's Repair Permissions Utility
Incorporated into OS X 10.2's Disk Utility, this functionality was also released in June 2001 for OS X 10.1.x as a stand-alone tools (available from the Apple's support web-site). Repair Permissions will restore system files to the 'proper' permissions (e.g. as with a freshly installed OS X system), however it will not restore missing or damaged files.
The corruption of permissions is NOT something that just 'happens' - usually someone has to take some action to alter the permissions of the system files and have sufficient privilege to override the existing permissions - generally not possible without supplying a password for authentication (to enable operating with the necessary System Administrator (root) privileges.)
If you receive 'Permission Denied' errors on system files, this program may 'fix' your system.
NOTE: If you have multiple OS X boot partitions on a system (which Apple claims is not supported), you may encounter a problem if attempted to check a boot partition other than the current one - this is future explained here.
OS X's: Booting in 'safe' mode
This feature introduced in OS X 10.2 instructs the OS X system to do an 'fsck -fy' at startup time instead of the normal 'fsck -p'. The latter invocation authorizes the program to make 'normal' repairs. If the program encounters problems which are outside what it considers 'normal' then it will stop, and ask for human intervention - telling the human to use the more powerful invocation as occurs when starting in 'safe' mode.
Power tools
(presented in alphabetic order)
These tools 'go beyond' what OS X's Disk Utility does and approach the problem differently by examining all the pieces and then verifying that the pieces match what the directory indices record as being present. For file systems which are very damaged, they may propose large changes - which is not necessarily a good thing - files may be recovered - but the directory structure may not.
Alsoft DiskWarrior (Mac OS 9 & earlier)
DiskWarrior is a one of the most trusted Classic Mac OS HFS and HFS+ file system repair tools in use. Current versions of DiskWarrior operate under Mac OS 9 and are supplied with a CD that boots the host into Mac OS 9.
- As of this writing, Apple has indicated that Macintosh computers introduced in the year 2003 will not be able to boot Mac OS 9 directly - preventing the use of the current version on new machines.
Micromat Drive 10 (Mac OS X)
Drive 10 is MicroMat's disk repair product and is an OS X native disk repair tool. The latest upgrade includes additional functionality over the initial release. This has utility has saved me a couple times, like when my PowerBook G3 crashed at MacWorld San Francisco 2002 - I took it back to the hotel, booted it from my iPod (which had OS X installed) and let Drive 10 do it's thing - which it did!
Search & Rescue
Your disk is hosed, what do you do? If it is to a point where you can't back it up, or fix the file system, etc.; because there are too many failures, then you need to take a different approach and attempt to 'rescue' the stuff you need off of the disk. If the disk has had a traumatic experience (fire, flood, run-over, etc.) then the only alternative is to send it out if you really need your data.
Prosoft Engineering's Data Rescue (Mac OS X and Classic)
Data Rescue is unlike the tools mentioned above as it is more concerned with recovering your information / files from a damaged file system or disk than to repair the fiile system, if the Disk Drive mechanism is functioning and you need to get information off of the disk, this is tool your last best chance to do-it-yourself. If a file system has been mistakenly re-initiailized or the drive's partitioning changed accidently, this utility is your best bet to recover the data, unlike the above tools, it does not modify the information on the disk - it merely extracts it .
DriveSavers data recovery service
Theory is you send these people a wad of cash, whatever remains of your disk drive, tell them what it used to be and if it can be done, they'll recover the data from it, stick it on another drive and send it back. (Check out the web site for their customer's horror stories.)
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