Storage and file systems, HFS and legacy, kSKDiskRoleLegacyMacData and kSKDiskTypeHFS

Discussion in 'macOS' started by grahamperrin, Oct 18, 2014.

  1. grahamperrin macrumors 601


    Jun 8, 2007
    Spun off from

    Curious. In logs for pre-release and released builds of OS X 10.10 Yosemite, this (for example):

    … OSInstaller[402]: Evaluating SKDisk { BSD Name: disk2s2 Mount point: / Role: kSKDiskRoleLegacyMacData Type: kSKDiskTypeHFS }

    If this is an indication that the HFS Plus file system is already, in some way, a legacy aspect of developments by Apple: I should not assume that what's to follow will be limited to Mac hardware. But if Macs begin to use something other than HFS Plus by default, I don't expect iOS to make the same transition at the same time.
  2. wrldwzrd89 macrumors G5


    Jun 6, 2003
    Solon, OH
    I noticed this myself, and I think you are on to something. My guess is btrfs.
  3. MikhailT macrumors 601

    Nov 12, 2007
    Not going to happen, BTRFS is under GPL. Apple refuses to accept GPL.

    Apple will build their own FS from scratch that'll take the best features from ZFS/BTRFS IMO.
  4. Mr. Retrofire macrumors 603

    Mr. Retrofire

    Mar 2, 2010

    HFS is deprecated, not HFS+ and HFS+J.
  5. grahamperrin thread starter macrumors 601


    Jun 8, 2007
    kSKDiskRoleLegacyMacData for all four types of HFS Plus, I guess

    The type for HFS+J is kSKDiskTypeHFS – a somewhat generic 'HFS' at the tail of that string.

    Without testing, it's reasonable to assume that all four types of HFS Plus are, for (at least) the purpose of installing OS X Yosemite:
    • type kSKDiskTypeHFS
    • role kSKDiskRoleLegacyMacData
    – that's legacy, not deprecated.

    (We should not expect Yosemite to install to a slice where HFS Plus is not journaled, but that's a separate topic.)

    Types of HFS Plus


    … Apple's hdiutil(1) Mac OS X Manual Page lists four HFS filesystem types for creation purposes:
    • HFS+
    • HFS+J (JHFS+)
    • HFSX
    • JHFS+X
    The less commonly used expression JHFSX is probably an informal abbreviation of JHFS+X.​

  6. sjinsjca macrumors 68020


    Oct 30, 2008
    Thanks for this.

    Since Lion, the file system has been gradually and steadily abstracted in both OS X and iOS. There has to be a reason. Looking at the ancient HFS family tree while comparing to the more modern file systems like BTRFS, ZFS and ReiserFS, OS X's file system looks positively dusty.

    Then there's the cloud. Fresh thinking is needed beyond the Dropbox model.

    Ergo, something is due. Apple isn't doing the abstraction just to keep its engineers busy.
  7. 556fmjoe macrumors 65816


    Apr 19, 2014
    Apple would do well to look at DragonflyBSD's HAMMER and HAMMER2 filesystems. I think they would be a very good fit for what Apple is trying to accomplish and they wouldn't have any licensing issues, since the code is under the DragonflyBSD license, not the GPL.

    Here's an example of some stuff you can do with HAMMER:

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