Mac OSX and Win XP cross-platform harddisks (filesystem)

Posted on 18 July 2012


After installing winXP bootcamp on my MBP I found that it can read the OSX disk, but also the Mac formatted external harddisks. This is because there is a HFS+ driver included with bootcamp. It’s read only and does not show the hidden apple files like the .Trashes. Then I bought the Seagate GoFlex for mac, that comes with a HFS+ driver for PC and a NTFS driver for mac. So I digged deeper into the matter of file systems.


There are a few different flavours of HFS:

  • First there is the old HFS, that’s much like the obsolete FAT file system because it has too many drawbacks. It has been replaced in 1998 and you don’t want to use it.
  • Since 1998 apple uses HFS+, also known as Mac OS Extended. You can store a maximum of 1 million TB on one disk, devided over a maximum of 4294 million files. You can use 255 UTF-16 characters per file. I don’t know what the maximum path length or depth is, but I read recommendations of max 220 for the total of folder names + file name.
  • Then apple added journaling: Mac OS Extended (HFS+) Journaled or HFSJ. This is the same system but now the OS keeps a journal for the disk, for data reliability. This is the default option. It’s safer, but also said to be slower. The listing in osX 10.5 and 10.6 is pretty confusing: they should not have mentioned HFS+ at all. This is exactly what they do since osX 10.8: the non-journaled option has disappeared.
  • Later case sensitivity (HFSX) was added, either with or without journaling. This is not supported by all apps, including the adobe suite, so you should only use it if you need to.
  • With Lion, filevault2 full disk encryption was added, either with or without case sensitivity.

As of Mountain Lion you can’t make NTFS, HFS or HFS+ disks anymore.

HFS Drivers for Windows

When you install windows on your mac with Bootcamp, it’s installed with HFS drivers for windows, but they are read-only. The drivers that came with my Seagate disk are the $ 20 Paragon HFS4win software, which can be downloaded here. Like the bootcamp HFS driver, it works with Windows’ IFS (Installable File System). This Paragon driver also has write access!

After installing it on the bootcamp Win XP, I could not only read, but also write to all mac OS formatted (both journaled and HFS+) harddisks, as well as the OSX partition in the MBP. It even shows the hidden files. Great! The only thing to do is point your default library locations to your OSX drive: Right click on a Library (say, Documents), and hit Properties. Hit the “Include a folder” button and navigate to the Documents folder in your osX home folder and then “Set Save Location” to set it as the default save location. Now you can work on your mac disk and from both windows on osX.

I have tested this with a HFSJ volume.  I don’t know if the Paragon HFS  driver supports filevault2 encrypted volumes?

note: With some disks I get this ‘do you want to check filesystem’ messages when I connect it. I got the Paragon v.9 driver with my drive. There are some damaged files on the disk, but this error is solved by using osX>disk utility>repair. It might have something to do with 255+ character filepaths? They are selling v.10 on their website, maybe that solves my problem?

There are many other read-only alternatives, but the only other known read/write solution for Windows is the $ 50 MacDrive software.

NTFS Drivers for osX

On mac, you have access to NTFS drives, but it’s read-only. If you also want write access, you can install the Paragon NTFS driver that comes free with a Seagate GoFlex for mac. After enabling it in system settings this driver provides read and write access to NTFS formatted harddisks. There goes my initial backup security system which relied on having NTFS drives that are read-only on osX.

After using it for a few weeks I feel like it is not very reliable. It could also be due to using an external firewire disk, but log and transfer to this NTFS disk did gave a lot of errors, which seems to be solved by switching to a mac formatted disk.

The free alternative is to install MacFuse and then install the free NTFS-3G driver. These systems might have been replaced, but these links could be a good starting point.

ExFAT as alternative?

Can we use an alternative filesystem for both windows and apple? FAT32 is limited (4GB max file size), NTFS is read only in mac, HFS+ needs additional drivers in windows, so what about ExFAT?

This filesystem is natively supported reliable with osX 10.6.5 and WinXP-SP2 and up. One drawback is that it might not work as boot-disk for these systems:

  • It is said that osX does not boot from it because it only supports ALC permissions, not the POSIX permissions.
  • It is said that Win7 can’t be installed on it due to several reasons including hard-links. Here is a workaround.

Another problem that it might not be perfect for data reliability:

  • osX implementation of ExFAT might result in corrupted files/volumes. See more here and here. This might have been solved with osX 10.8? Here is a repair tip.
  • It’s less reliable then FAT32 because it only uses one allocation table. This is a potential problem mainly for external volumes that could be disconnected accidentally. To use alternating allocation tables and free space maps, you need to us the optional TexFAT component.
  • ExFat is designed for flash, not for the >500GB moving-parts HDD’s. Journaling (for data safety) and compression (for archiving) are not part of exFat, like it is of NTFS and HFSJ. On the other hand, there are also forum posts explaining why exfat is better then NTFS or HFSJ.

Then some usability limits:

  • ExFat might not be supported by all software encryption like filevault2 or compression systems like NTFS. I like hardware encryption.
  • ExFat has a limit of only 2,8 million files per directory. For me, that’s fine.

To finish there is the cluster size. NTFS has a 4K cluster size, but exFAT has 64K-32M (256K was selected as default, but the windows help states 128K as default for for 32GB+ drives). The smaller the cluster, the more efficiently the disk stores your data, but it might be slower. On the other hand, you can only address a limited number of clusters (!?). It really comes down to performance v.s. wasted space. For now I stick with 256K.

Conclusion: use HFS+ for osX system drives, but start testing with ExFAT for data drives.


exFAT has license limitations. The UDF file format is an open standard, supported by both windows and apple. It supports up to 255 characters (unicode only) and POSIX permissions management. It’s developed originally for DVD’s but there are several suggestions that their plain profile might also be interesting for HDD and flash storage.

Posted in: Computers