How can I format a USB "thumb drive" so it will be readable on OS X and Windows?

Question

I have an OS X system. I want to use it to put some files on a USB drive and then be able to loan the drive to Mac and XP and Vista users so they can get the files off it.

I also need to wipe the drive clean first to make sure there's nothing sensitive on it by accident because I'm going to be passing it around.

What the name of the filesystem format I want? What's the procedure?

Command line operations are fine.

Answer 1

You want to format the drive using Fat32, which is most readable. I'm not sure about the Mac procedure, but to format the drive in Windows you right click on it in (My) Computer and select "Format..." Set the file system to Fat32 (it should be the default, but you should make sure). Also make sure that "Quick Format" is UNselected, as it does not erase the data. Then click OK and it will start formatting the drive. It will warn you, but I'm going to reiterate (preiterate?) DO NOT REMOVE THE DRIVE AT THIS TIME. Also be aware that this will remove all the files, though not necessarily securely.

Also, depending on the sensivitity of the information and the people you are afraid might read it, you might want to do further erasing procedures. I know that the Mac allows you to delete files securely. You need to do this BEFORE reformatting the drive, or there will be no files to erase securely.

EDIT (years later): You might also try formatting the flash drive UDF. This is harder than formatting it FAT32, but can store large files and has some other nice features. Since UDF is a file system that optical discs (CD, DVD, etc.) often use, it is understood by all major OSs.

Answer 2

If you're automating this under OS-X, the following might be useful.

First, Find the disk you care about using diskutil list:

/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *3.9 GB     disk1
   1:                 DOS_FAT_32 UNTITLED                3.9 GB     disk1s1

Note the IDENTIFIER column; the shorter one (in this case, disk1 is the whole disk; the longer ones e.g. disk1s1 are volumes on that disk).

Pass the name of the disk you want to wipe to this script:

    #!/bin/bash

disk=$1
if [ -z "$disk" ]; then
    echo I need you to give a disk to wipe, e.g. disk1
    exit 1
fi

diskpath=/dev/$disk

diskutil unmountDisk $diskpath
if [ "$2" == "secure" ]; then
    echo Wipe of disk requested before format...
    diskutil zeroDisk $diskpath
fi

echo Partitioning...
diskutil partitionDisk $diskpath 1 MBRFormat FAT32 UNTITLED 100% 

diskutil list $diskpath
diskutil mountDisk $diskpath

This will re-partition the disk to have one large FAT32 volume on an MBR-partitioned disk; if you pass "secure" as well, it'll zero-wipe the disk for added security.

Examples:

• ./wipedisk.sh disk1 will make disk1 have one partition (disk1s1) formatted FAT32
• ./wipedisk.sh disk2 secure will zero disk2 and then create a FAT32 partition (disk2s1)

Answer 3

On leopard, you can use DiskUtility to format a volume as fat32.

1. Insert the usb drive
2. Launch Disk Utility from /Applications/Utilities/
3. Select the drive on the left pane
4. On the right pane, click on the Erase tab
5. Choose Volume Fomat as MS-DOS(FAT)
6. Click Erase

If you are storing particularly sensitive data on the drive, you may want to perform a "Secure Erase" instead -- to do this, after step 5 above, do:

1. Click [Security Options...]
2. Move the slider one spot to the right (this is sufficient for all modern drives)
3. Click [OK]

Now proceed with Step 6 above. This fills the disk with zeroes before performing the format; it takes a while, but ensures that data is actually erased rather than just marked as erased.

Note that with modern flash media, even this step is not entirely reliable and data recovery may be possible. You have to weigh the trade-offs you're willing to make.

Answer 4

exFAT is a better solution. It's specifically designed for USB drive and fully supported by MacOS now. More importantly, it supports files larger than 4GB

Answer 5

If you want to use the drive with Windows, you can choose between FAT32 or NTFS. FAT32 gives great compatibility with about everything, but cannot store files larger than 4 GB. NTFS can be read under OS X by default starting with 10.3 (from 2003), and read/write access is possible since 10.6 using an unsupported, hidden function (or external tools). Source

To wipe the disk, I would suggest to use a separate disk wiping/secure erasure utility, or simply Linux with the "dd" command. Make sure to erase the entire stick, not just the files, to avoid residue. This will reliably prevent recovery using standard recovery tools.

If you are afraid that someone might disassemble the stick and scrape data off using special hardware (or undocumented low-level interfaces), the only reasonable way to "wipe" it securely to prevent that is physical destruction of the flash module.