PatchLog

I just got the biggest slap from MacOSX. Yes, I was punished for my ignorance.  I had not idea that the HFS filesystem defaults to case insensitive. I thought it would be case sensitive like in Unix but no.

When I first saw it I didn't believe it. The first clue was when I ran mysql_install_db an I got some warnings about about the filesystem being case insensitive. I didn't believe it because I knew I was able to create files with lower and upper cases so I just ignored it.

The confusion comes from the fact that the HFS+ filesystem is  MyFile.txt would be the same as myfile.txt .  The filesystem preserves cases so it will remember the original file name and a ls will show that but you would be able to access the file with different names. At the first glance this seems like a neat feature but it can actually create big problems when you're interacting with files from case sensitive filesystems.

The slap came from using rsync to backup files from a Linux machine to a macmini machine.   Just imagine a directory with many files split over directories from a to z and A to Z on Linux, something like files/a , files/A, files/b, files/B .

Now rsync -avz -e ssh  files/  backup@macmini:~/files/   and you'll end up with a folder named files on macmini but it will only have the upper case subfolders. The files in the lower case subfolders would be put in the upper case subfolders. This if really bad, it can really break consistency and mess up the data ( imagine different files with the same name one in A and the other in a as just one of the possibilities, there are other like this)

So now, what ? Reformat and change the filesystem to be case sensitive and journaled for easier recovery.
Be careful the next operation will remove all data on your disk:

 
 diskutil eraseDisk "Case-sensitive Journaled HFS+" DiskName YourDiskId

YourDiskId is the disk that you want to erase.It can be disk1, disk2,etc... Look for it using diskutil list

This entry was posted on Wednesday, March 26th, 2008 at 12:17 pm and is filed under MacOSX. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.