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Make OS X see expanded space in RAID setup Storage Devices
I expanded my RAID from 9TB to 13TB, and after it had finished, I noticed I had to resize the partition in order to use the new space. When I used Disk Utility, I got an error saying "Partition failed with the error: MediaKit reports partition (map) too small." After googling, I found the solution on the "life as i know it" blog, and thought I'd share the basics of the solution.

From the blog post, here's the essence of the problem and the solution:
Basically whatís going on here is that the GPT table is built only big enough for the drive itís on. Thatís a logical assumption - hard drives donít magically get larger - unless theyíre RAID arrays. Weíre just removing the GPT partition information, and replacing it. Should things go crazy, as long as youíve got the start and size information for the partition you care about, you should be good. No guarantees obviously, but Iíve done this three times and no data loss yet.
Read on for a summary of the fixes involved, and see the blog post for more details...

Here are the basic steps involved in expanding a RAID setup:
  1. Open Terminal and run df. Note the mount point for the drive youíre trying to expand, something like /dev/disk3s1. The disk3 is the relevant bit.
  2. In Disk Utility, unmount the current partition on the disk to be expanded.
  3. In Terminal, run sudo gpt show /dev/disk3, where disk3 is the value from the first step. In the output, copy the values for start and size from the line with the largest size value.
  4. In Disk Utility, unmount the partition again.
  5. In Terminal, run these commands:
    $ sudo gpt destroy /dev/disk3
    $ sudo gpt create -f /dev/disk3
    $ sudo gpt add -b nnstart -s nnsize /dev/disk3
    Replace nnstart and nnsize with the values from step three.
  6. Reboot your Mac, then use Disk Utility to resize the partition.
[robg adds: I can't test this one, lacking a RAID setup. Note that I rewrote most this hint to provide a summary of the blog post; the original submission was simply a copy of the blog entry, which I couldn't use as is without permission from the blog owner.]
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Make OS X see expanded space in RAID setup
Authored by: designr on Nov 18, '09 11:59:55AM


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Make OS X see expanded space in RAID setup
Authored by: systemsboy on Nov 18, '09 12:24:07PM

This is a great hint. I've set up Apple-branded RAIDs in the past (pre-Intel) and was astounded to learn that, despite what it says in the literature, expanding the RAID volume is not practically possible because of the AFP file system and the APM partition map, which are not expandable.

It's great to see that there's finally a workaround for this problem, but I wanted to add one caveat: this procedure uses the gpt command (GUID partition table maintenance utility), which I'm pretty sure means that your disk must be formatted with the GUID Partiton Table.

To find out what partition table your disk is using, open Disk Utility, select the disk (the device, not the partition) and press the Info button (or hit command-i). The third line is the Partition Map Scheme. If it says GUID Partition Table, you should be good.

If it doesn't, I don't think this hint will work for you.


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