Change drive "block size" to 4096 I just bought a 4tb hard drive and enclosure and attempted to encrypt it with truecrypt. I errored with a message saying the block size must be 4096 bytes for >2TB drive.

How do i alter the drive to have that block size? 

Currently it says block size is 512

diskutil info /dev/disk2s2|grep "Block Size"
   Device Block Size:        512 Bytes
Format the drive using Disk Utility. Find out what disk identifier the drive has (/dev/disk0, /dev/disk1, /dev/disk2, etc…). You can do so in Disk Utility.

Then use the command line tool newfs_hfs to create a new HFS file system on the disk. The command below is taken from here.

newfs_hfs -v HFS_VOLUME_NAME -b 4k /dev/rdisk2s1


This creates a HFS volume with name "HFS_VOLUME_NAME" and a block size of 4k on the device with identifier disk2s1.