How can I remove the Mac recovery partition from an external drive?

Question

My early 2011 MBP came with a 500 GB HDD, which I recently changed out for a 128 GB SSD. The old internal drive now serves as a backup drive... however... I'd love to get rid of that Recovery HD partition so that I can A) use the space, and B) stop being asked about ejecting multiple partitions when I eject the drive.

Yes, I've seen this question which is almost a duplicate, except my situation is a little different and I don't want to break anything!

Some output from my terminal:

Macbook-Pro:~ matt$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *128.0 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:          Apple_CoreStorage                         127.2 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS OS X                   *126.8 GB   disk1
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk2
   1:                        EFI                         209.7 MB   disk2s1
   2:          Apple_CoreStorage                         499.2 GB   disk2s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Backup                 *498.9 GB   disk3
Macbook-Pro:~ matt$ 

... and I'm confused, because I only have my internal, 128 GB SSD and my external, 500 GB HDD connected at the time I ran this. My question is two-fold:

1. Why are there 4 disks showing up in diskutil list? I only have the two physical drives connected... what do the * characters mean? Ultimately, which disk should I be re-partitioning?

2. How can I safely remove the recovery partition on my now-backup-only drive? Of course I want to keep the one on my 128 GB drive, so obviously I won't mess with disk0 or disk1... I assume this will involve the same/similar steps as in the question I linked to above.

Just wanted to be sure before I did anything potentially destructive... cheers for your advice.

Answer 1

Your disk1 and disk3 are the virtual disks created by CoreStorage, that is, the system underlying FileVault 2 (full disk encryption). This is why your data partitions on the "real" disks (disk0 and disk2) have type Apple_CoreStorage.

The recovery partition on your external drive is this one:

   3:                 Apple_Boot Recovery HD             650.0 MB   disk2s3

Deleting it may however not be a good idea. Because CoreStorage drives are encrypted, the bootloader can't read any data from them - the OSX kernel (with the CoreStorage driver) needs to be loaded to ask for the user password, which opens up the main drive containing the rest of the operating system and data. So with CoreStorage enabled, the Recovery HD partition doubles as an unencrypted boot helper.

I don't have much experience with CoreStorage, and you haven't made it completely clear what your backup disk contains. I know that unencrypted Time Machine disks are bootable. I would imagine that encrypted ones are, too, with the caveat of requiring a boot helper, but I don't know for sure. Furthermore, since you only mention "backups", maybe you're using a different backup system which may or may not be bootable.

If your backups are not intended to be bootable, I think you should be able to delete the Recovery HD, although there is a certain risk that CoreStorage relies on it nevertheless. If they are bootable, deleting it outright will make them fail to boot. You could try writing the partition parameters displayed by gpt show disk2, deleting the partition using gpt without overwriting it, rebooting, and checking that it still works, and recreating it with the exact parameters (again using gpt, not diskutil) if you have trouble accessing your backups.

However, boot helpers don't actually need to contain a full recovery system. Prior to OSX Lion, boot helpers (e.g. used for software RAID) were always 128MiB in size, and this is still enough for Lion and Mountain Lion. Still, recreating a deleted boot helper isn't exactly straightforward.

Then there's the question of what you'll do with the extra ~520MB you gained. I don't think you can resize core storage partitions, so all you'll be able to do is create a ~400MB additional partition, which isn't terribly useful.

Overall, I'd say it's not worth the risk/trouble to gain ~500MB.