How to Resolve POSIX error during Mac HDD Partitioning?

Simple Mac operations never ask for any expertise. Some unavoidable circumstances check our patience in fighting the difficulties against completing those easy tasks. If you are using Mac for more than a year then you must have tried partitioning & formatting Mac hard drive, external drive or a USB flash media and faced different unknown errors. There is an impression that many of us like to use hard drives on both (Mac and Windows) platforms and format drive with the exFAT file system. Please keep in mind, if you want a USB drive to be accessible on both platform then format the drive on PC platform rather Mac because OS X system makes USB drive unreadable while erasing with exFAT type. 

There is a simple and standardized way to format and partition Mac. Please don’t partition a volume if that is in use. Although partitioning & formatting drive can be done manually with these easy steps mentioned below:

Step 1: Go to Disk Utility (Applications>> Utilities>> Disk Utility)

Step 2: Select your drive (which need to format) from the left sidebar

Step 3: Click on the Partition tab above top side in the DU main window

Step 4: Decide the number of partitions from the drop down menu to 1 or 2..

Step 5: Click on Options tab and set the partition scheme to GUID and click ok button

Step 6: Set the format type to Mac OS Extended (Journaled) and click Partition button.

Disk Utility window

Step 7: Once the new partition creation process gets completed, select the new volume from the left side and click Erase tab from the main DU window

Step 8: Again set the format type to Mac OS Extended (Journaled) option. Click on the Security button and then ok button to return back to the main window with Erase tab

Now, click on Erase button and wait until the process finish

The above mentioned USB drive formatting steps seem so simple but user face different error like Disk Utility POSIX error, disk can’t be partitioned, can’t allocate memory, disk erase failed etc.

On the other hand, to troubleshoot the complex errors, Mac users try different methods like reset devices, performs SMC resetting, and PRAM reset methods but get no fruitful response. If you are one of those users who are facing error while partitioning hard drive or any external drive then please scroll down. 

Nowadays Mac user is aware about the built-in Terminal app and flexible with the method of executing few commands. Terminal app can be used alternatively to get rid from the drive partitioning enrage errors.

Before proceeding towards Terminal window, go to Disk Utility and find the ‘Disk Identifier’ value of the attached USB drive. To get it done, select the drive from DU main window. Click on “info” button. A Pop up window will prompted. Copy the Disk Identifier name field value from there.

Terminal application

After getting the Disk Identifier value, open Terminal (go to Applications>> Utilities and double-click on Terminal) and execute the below mention commands to format drive

find disk identifier value in red circle from Disk Utility

Command 1:  diskutil

diskutil eraseVolume HFS+ NAME IDENTIFIER

type this command in Terminal window and replace the NAME with the drive name and IDENTIFIER with the identifier name (disk ID got earlier from Disk Utility window)

Command 2:  fdisk

Here is one more alternate text-based command to partition and set up the drive apart from the above one. Replace IDENTIFIER word with the ID found in Disk Utility and keep the rest command same and press enter

fdisk -a hfs /dev/IDENTIFIER

Note: [if you don’t know the device name then please use this command fdisk -l and hit enter]

Once both the commands get executed, goto Disk Utility and try to manage drive again simply.