Mac – How to format multiple exFAT partitions on USB drive

disk-utilityexfatmacpartitionusb

I'm following the instructions in Creating a bootable Clonezilla dual partition USB device but using my Mac laptop running El-Capitan.

I managed to create an MBR partition table and two partitions on the external USB drive using OSX' fdisk utility but I failed to find a way to format the existing partitions to ExFAT.

All the references I found so far point to diskutil eraseDisk or suggest using Windows or Linux for that, but I don't have access to bare-iron servers with these OS's and failed to access the unformatted USB drive from VirtualBox virtual machines on my laptop.

So, the question is – "Is there a way to execute the equivalent of mkfs.vfat -F 32 /dev/sdb1 on OS X?"

Best Answer

To format an ExFAT partition, unmount the partition and use (sudo) newfs_exfat [options] /dev/disk*s*. Check man newfs_exfat for the options.

The default FAT-size is 32bit, so you don't have to (or more precisely: you can't easily) specify the -F option.

Typically the Terminal commands should look like this:

diskutil list #to get the disk identifier of the exFAT partition
diskutil unmount /dev/diskxsy
sudo newfs_exfat -v Name /dev/diskxsy

Related Solutions

MacOS – How to move Mac and Windows partitions to single Hard Drive

Before you start, make sure you have a verified working clone of both partitions/systems.

You will ideally want to have software that can clone partitions, such as either the excellent CarbonCopyCloner, or the equally awesome SuperDuper, both of which will allow for your needs (complete clone) in their Shareware mode. I don't know what tools are suitable for PC, but find one that does the equivalent for Windows installations.

Reboot from your cloned Mac OSX installation, and prepare to repartition your target Hard Drive. Disk Utility can sometimes repartition volumes non-destructively, but for this I would recommend quick erasing the drive and repartitioning to the desired sizes for each OS, with a caveat for the situation below.

Repartition as desired (ensure GUID, journaled, case-insensitive for the Mac Volume), noting you may need to go through various procedures if you are using OSX 10.7 Lion and wish to retain the hidden recovery partition (ie: you may have to reinstall Lion and restore from your backup, then proceed with Bootcamp installation which will again walk you through creating a suitable PC formatted boot volume which you can later clone your Windows installation back to).

Clone back the OSX Installation that you are booted from to the target Mac partition on the internal drive (if you haven't already restored from this in the previous step). Do the equivalent process in Windows for your Windows installation.

Test each by booting into each and making sure everything works as expected.

MacOS – How to fix Mac hard drive partition showing as FDisk_partition_scheme

Please try the following:

Get the disk identifier of your external 3 TB drive
```
diskutil list
```
Below I assume the disk identifier is disk6
unmount the disk:
```
diskutil umountDisk disk6
```

Overwrite the first 40 blocks:

sudo dd if=/dev/zero of=/dev/disk6 bs=512 count=40

Create a new gpt:
```
sudo gpt create /dev/disk6
```

Check the disk info with:

diskutil info /dev/disk6

Reassure yourself that the device block size still is 512 Bytes

You may also use

sudo gpt -r show /dev/disk6

If the gpt shows:

   start        size  index  contents
       0           1         PMBR
       1           1         Pri GPT header
       2          32         Pri GPT table

you have a disk & disk controller which report a logical block size of 512 Bytes. Please continue with the next step.

If the gpt shows:

   start        size  index  contents
       0           1         PMBR
       1           1         Pri GPT header
       2           4         Pri GPT table

you have a disk & disk controller which report a logical block size of 4096 Bytes. Please stop here and add a comment.

First rebuild the EFI entry with:
```
sudo gpt add -b 40 -i 1 -s 614400 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk6
```
Depending on the size of the disk and the system version differently sized EFI volumes are built if partitioned with Disk Utility: either one with the size 200 MiB or one with 300 MiB. Here it's obvious that your disk contains a 300 MiB EFI and probably 4096 bytes of unallocated disk space: (314598400-1024)/512=614448 (=Start block main volume) 614448-40-8=614400 (=size of EFI)
Rebuild your main volume with:
```
sudo gpt add -b 614448 -i 2 -s SizeOfVolume1 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk6
```
The size of the main volume can be determined by the first (corrupted & old) entry of the second GPT table: (3000592961536/512)=5860533128 is its block number. Then the size is calculated by 5860533128-614448=5859918680 blocks. Since 5859918680 is dividable by 8 (4096 physical block size/512 logical block size) this is a good guess for the volume size.

The best guess is finally:
```
sudo gpt add -b 614448 -i 2 -s 5859918680 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk6
```
The second best guess is:
```
sudo gpt add -b 614448 -i 2 -s 5859918672 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk6
```
Probably your lost volume gets mounted now. Verify the volume with:
```
diskutil verifyVolume disk6s2
```
If necessary try to repair the volume.
```
diskutil repairVolume disk6s2
```

Since you moved the "corrupted" disk to a different case and disk controller the logical block size was modified. The old partition map is probably based on a logical block size of 4096 Bytes.

To recover the partition map in the old (4096b) case you would had to enter the following to restore the GPT (based on David Anderson's answer):

Create a new gpt:
```
sudo gpt create /dev/disk6
```

First rebuild the EFI entry with:

sudo gpt add -b 6 -i 1 -s 76800 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk6

Rebuild your main volume with:

sudo gpt add -b 76806 -i 2 -s 732457067 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk6

the final partition map looks like this:

 sudo gpt -r show disk1
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2           4         Pri GPT table
           6       76800      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
       76806   732457067      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
   732533873       32768         
   732566641           4         Sec GPT table
   732566645           1         Sec GPT header

Based on the 4096b part this "retranslates" after installing the disk in a 512b logical block size case to:

Create a new gpt:
```
sudo gpt create /dev/disk6
```