Booting a MacBook Pro from an SDHC Card

I recently picked up an ExpressCard/34 SD reader along with a Transcend 16GB SDHC card. The reader was to ease the transfer of photos from a digital camera and the high-cap SDHC card ensures I can take plenty of photos without shuffling about cards.

With the recent announcement of SD-slot-ness MacBook Pros (drool) that can boot from the SD slot, it made me wonder if a previous generation MacBook Pro could do so, too.

And it can! Which isn’t totally surprising. SD ExpressCard readers effectively act like USB drives and most (all?? I don’t know) Intel macs can boot from USB devices.

On the click through is instructions for formatting an SD car correctly and slapping down a bootable image.

Given the relatively low prices of SD cards, I’m making a habit of carrying around a “rescue card”. Tiny enough to not be noticeable, can be reformatted to use as photo-space trivially, one hell of a lot of tougher than optical media, and will prove to be indispensable if I ever need it.

Out of the box, an SD card will be formatted with an MS-DOS (FAT) filesystem.

Useless (except for in digital cameras).

But it isn’t enough to just reformat it to be an HFS+ Journaled filesystem. You also need to change the partitioning table.

To do so:

  • Launch Disk Utility
  • Insert the SD card
  • Select the volume (labeled 16.06 GB Generic STORAGE DEVICE Media in my case)
  • Select the Partition tab
  • Select 1 Partition from the Volume Scheme. Even if there is only one partition, selecting 1 Partition will enable the all critical Options… button at the bottom
  • Click Options… and select GUID Partition Table.
  • Make sure the partition will be formatted as Mac OS Extended (Journaled)
  • Click Apply

You now have an SDHC card ready to be made bootable. From here, you could install Mac OS X to the card, install something like a DiskWarrior bootable image to the card, copy an already bootable partition to the card or blast down a bootable DMG to the card.

Disk Utility makes it trivial to clone whole volumes from one partition to another. If you do so, make sure and check erase destination as that will ensure that Disk Utility uses a block based copy and, thus, is about a zillion and twenty times faster.

If you have a bootable disk image around, you can easily use Disk Utility to restore the image to the partition or you can use the command line:

sudo asr -source /path/to/bootable.dmg -target /Volumes/SDCard -erase -noverify -noprompt

Then, reboot your mac and hold down the option key. The newly created boot partition should show up.

It is fast enough to boot for installation, recovery, or intermittent use.

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One Response to “Booting a MacBook Pro from an SDHC Card”

  1. don delwood says:

    i’ve purchased several USB sticks and apparently some of them are bootable and some are not. i’ve run into this problem while trying to boxee my apple TV (ATV).
    (podcast: syst/m discusses this, however, their answer is “trial and error”)

    however, i never tried the GUID table option.

    do you know if this is the real issue between bootable USB sticks or is the problem somewhere else?


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