_______ ____________ _______ _\__ /_________ ___ _____ | _ _ \ _ | ____\ _ / | |/ _ \ | / / / / | | | /___/ _ | | / / |___/___/ /___/____|________|___ | |_| |___|_____/ \__/ |___|

1. run fsck

First, we need to make sure the disk is clean, so force a disk check using fsck. This can take a while!

# fsck.ext3 -f /dev/sdf1
e2fsck 1.41.11 (14-Mar-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
usb2: 374137/61054976 files (2.1% non-contiguous), 89863648/244190000 blocks

2. run resize2fs

Next, we run resize2fs to scale the volume to the requested size. As I used less than 400GB, I found this a good value. This took a few hours on my system:

# resize2fs /dev/sdf1 400G
resize2fs 1.41.11 (14-Mar-2010)
Resizing the filesystem on /dev/sdf1 to 104857600 (4k) blocks.
The filesystem on /dev/sdf1 is now 104857600 blocks long.

3. run fsck

To make sure everything is OK, we have to re-run fsck, again, this takes some time:

# fsck.ext3 -f /dev/sdf1
e2fsck 1.41.11 (14-Mar-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
usb2: 374137/61054976 files (2.1% non-contiguous), 89863648/244190000 blocks

4. partition

Now I used fdisk to remove all partitions, and resize the first one. After that I created a HFS+ file system on the remainder of the disk:

# fdisk /dev/sdf

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): p

Disk /dev/sdf: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x53038aec

   Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1      121601   976760001   83  Linux

Command (m for help): d
Selected partition 1

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-121601, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-121601, default 121601): +400G

Command (m for help): p

Disk /dev/sdf: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x53038aec

   Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1       52218   419441053+  83  Linux

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (52219-121601, default 52219):
Using default value 52219
Last cylinder, +cylinders or +size{K,M,G} (52219-121601, default 121601):
Command (m for help): p

Disk /dev/sdf: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x53038aec

   Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1       52218   419441053+  83  Linux
/dev/sdf2           52219      121601   557318947+  83  Linux

Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): af
Changed system type of partition 2 to af (HFS / HFS+)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

# hformat -l Backup /dev/sdf2
Volume name is "Backup"
Volume was created on Thu May 27 08:28:53 2010
Volume was last modified on Thu May 27 08:28:53 2010
Volume has 2113961984 bytes free

Now, I created a HFS volume, but it did not work! I tried converting it to HFS+ using Apple’s Disk Utility, but no luck here either:

May 27 08:29:29 blade Disk Utility[22152]: newfs_hfs: /dev/rdisk2s2: partition size not a multiple of 4K.

5. MBR to GPT

MBR partition tables use a pre-defined block size of (heads * cylinders), which doesn’t align with 4K blocks. With GPT you can manually allocate the number of sectors allowing you to choose proper 4K blocks. Back to Linux I installed the gdisk utilitity which can do the conversion for you. Firstly, remove the HFS partition:

# fdisk /dev/sdf

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): p

Disk /dev/sdf: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x53038aec

   Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1       52218   419441053+  83  Linux
/dev/sdf2           52219      121600   557310915   af  HFS / HFS+

Command (m for help): d
Partition number (1-4): 2

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Now we can use gdisk to convert the partitioning header:

# gdisk /dev/sdf
GPT fdisk (gdisk) version 0.5.1

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present


***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format.
THIS OPERATON IS POTENTIALLY DESTRUCTIVE! Exit by typing 'q' if
you don't want to convert your MBR partitions to GPT format!
***************************************************************

ommand (? for help): p
Disk /dev/sdf: 1953525168 sectors, 931.5 GiB
Disk identifier (GUID): 6B9DAEFC-F7AE-0F1A-7028-A497B320B10C
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1953525134
Total free space is 1114642994 sectors (531.5 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              63       838882169   400.0 GiB   0700  Linux/Windows data

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
MBR PARTITIONS!! THIS PROGRAM IS BETA QUALITY AT BEST. IF YOU LOSE ALL YOUR
DATA, YOU HAVE ONLY YOURSELF TO BLAME IF YOU ANSWER 'Y' BELOW!

Do you want to proceed, possibly destroying your data? (Y/N) y
OK; writing new GPT partition table.
The operation has completed successfully.

Now we can create a nice 4k-block partition. As you can see there are 1114642994 free sectors. To convert this to a 4k-block partition, you can use a simple calculation:

# python
Python 2.5.1 (r251:54863, Feb  6 2009, 19:02:12)
[GCC 4.0.1 (Apple Inc. build 5465)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> divmod(1114642994, 4096)
(272129, 2610)
>>> 4096 * 272129
1114640384

So our new partition size will be 1114640384 sectors:

# gdisk /dev/sdf
GPT fdisk (gdisk) version 0.5.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/sdf: 1953525168 sectors, 931.5 GiB
Disk identifier (GUID): 6B9DAEFC-F7AE-0F1A-7028-A497B320B10C
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1953525134
Total free space is 1114642994 sectors (531.5 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              63       838882169   400.0 GiB   0700  Linux/Windows data

Command (? for help): n
Partition number (2-128, default 2): 2
First sector (34-1953525134, default = 838882170) or {+-}size{KMGT}:
Last sector (838882170-1953525134, default = 1953525134) or {+-}size{KMGT}: 1953521664
Current type is 'Unused entry'
Hex code (L to show codes, 0 to enter raw code): af00
Changed system type of partition to 'Apple HFS/HFS+'

Command (? for help): p
Disk /dev/sdf: 1953525168 sectors, 931.5 GiB
Disk identifier (GUID): 6B9DAEFC-F7AE-0F1A-7028-A497B320B10C
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1953525134
Total free space is 3499 sectors (1.7 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              63       838882169   400.0 GiB   0700  Linux/Windows data
   2       838882170      1953521664   531.5 GiB   AF00  Apple HFS/HFS+

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
MBR PARTITIONS!! THIS PROGRAM IS BETA QUALITY AT BEST. IF YOU LOSE ALL YOUR
DATA, YOU HAVE ONLY YOURSELF TO BLAME IF YOU ANSWER 'Y' BELOW!

Do you want to proceed, possibly destroying your data? (Y/N) y
OK; writing new GPT partition table.
The operation has completed successfully.

6. round up

Now plug the disk into your Mac and use Disk Utility to erase the partition using HFS+ with journaling. This created a workable HFS+ partition in a few seconds.

Also, just to be sure, I ran fsck on my Linux partition again, the disk mounted cleanly after this and all data was still available after the transition.