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macrumors newbie
Original poster
Apr 24, 2011
Can anyone tell me how to reverse this back to a usable format that i can read and write to?

Disk Utility:
Mount Point : /Volumes/USB Capacity : 7.3 GB (7,816,085,504 Bytes)
Format : ISO 9660 (Rockridge) Available : 0 Bytes
Owners Enabled : No Used : 2.6 GB (2,802,634,752 Bytes)
Number of Folders : 0 Number of Files : 0

* Btw if it helps there are plenty of folders and files on this usb and tons of free space but Disk Utility begs to differ?


macrumors Westmere
May 16, 2008
You need to format it as HFS+, exFAT or FAT32. OS X can read NTFS drives, but not natively write, unless you enable that via 3rd party software.

Format A Hard Drive Using Disk Utility (which is in your /Applications/Utilities folder) Choose the appropriate format: HFS+ (Hierarchical File System, a.k.a. Mac OS Extended (Journaled) Don't use case-sensitive) NTFS (Windows NT File System)
  • Read/Write NTFS from native Windows.
  • Read only NTFS from native Mac OS X [*]To Read/Write/Format NTFS from Mac OS X, here are some alternatives:
    • For Mac OS X 10.4 or later (32 or 64-bit), install Paragon (approx $20) (Best Choice for Lion)
    • For 32-bit Mac OS X, install NTFS-3G for Mac OS X (free) (does not work in 64-bit mode)
    • For 64-bit Snow Leopard, read this: MacFUSE for 64-bit Snow Leopard
    • Some have reported problems using Tuxera (approx $36).
    • Native NTFS support can be enabled in Snow Leopard and Lion, but is not advisable, due to instability.
  • AirPort Extreme (802.11n) and Time Capsule do not support NTFS
  • Maximum file size: 16 TB
  • Maximum volume size: 256TB
  • You can use this format if you routinely share a drive with multiple Windows systems.
exFAT (FAT64)
  • Supported in Mac OS X only in 10.6.5 or later.
  • Not all Windows versions support exFAT. See disadvantages.
  • exFAT (Extended File Allocation Table)
  • AirPort Extreme (802.11n) and Time Capsule do not support exFAT
  • Maximum file size: 16 EiB
  • Maximum volume size: 64 ZiB
  • You can use this format if it is supported by all computers with which you intend to share the drive. See "disadvantages" for details.
FAT32 (File Allocation Table)
  • Read/Write FAT32 from both native Windows and native Mac OS X. [*]Maximum file size: 4GB.
  • Maximum volume size: 2TB
  • You can use this format if you share the drive between Mac OS X and Windows computers and have no files larger than 4GB.


macrumors Penryn
Feb 20, 2009
Well, if Disk Utility can't initialize it -- my suggestion would be to get another flash drive...
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