I've been asked to format a USB Drive with a larger Allocation Unit Size than the default. I'm using a Mac, Snow Leopard. In Disk Utility, I am unable to see anything to do with Allocation Unit Size. A bit of Googling suggests it might be called Cluster Size, but I can't see anything for that, either. Does anyone know if it's possible to format a drive with FAT and use a larger than default Allocation Unit Size / Cluster Size?
You should be able to do this from a command line using the
newfs_msdos command. For example:
#> newfs_msdos -F 32 -V somevolumename /dev/youdiskdevice
The command takes many arguments that you may want to explore..
-c cluster-size for example.
I am sure you could google around for newfs_msdos for some usage examples and also
Hope this helps!
For example to format FAT32 with 64kb allocation unit size:
sudo newfs_msdos -F 32 -c 128 -v VOLUMEID /dev/yourdiskdevice
with 32kb allocation unit size should be use 64 cluster size:
sudo newfs_msdos -F 32 -c 64 -v VOLUMEID /dev/yourdiskdevice
I didn't know that I had to
unmount the disk in order to format the card. So I looked around to find an answer for the different errors, when all I actually needed to do was
diskutil unmount /dev/disk(the ident number)
I had to format my micro SD for a sports cam and the "cluster" size was wrong. I tried the
-c 32 first, no joy.
-c 64 Bingo!