Formatting hard drive question

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Level 1

8 points

Formatting hard drive question

I've got an early 2011 MacBook Pro that is currently running OS X El Capitan. About a year ago, my hard drive failed and I replaced it with a Samsung SSD. I've had no problems at all but I'm wanting to format this drive before I upgrade to Sierra as there's loads of stuff on here that I want rid of! I'm just a bit confused about what to do though. When going into Disk Utility after restarting my Mac, in the right hand column where you select the drive, I get the SSD, but there is also one called OS X Base System? What is this? Can I get rid of it? Also, if I do format the SSD, how do I go about getting OS X back onto it. When I first put it in, there was some sort of internet recovery thing I think, will it just be the same procedure?

Thanks!

MacBook Pro (15-inch Early 2011), OS X Yosemite (10.10.3)

Posted on Oct 10, 2016 12:49 PM

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Answer 1

Oct 10, 2016 1:14 PM in response to macca-uk

I am assuming that when you say "going into Disk Utility after restarting my Mac" you're rebooting into recovery mode, and using Disk Utility from within that. From within recovery mode you will be able to erase the drive and then install the OS.

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Answer 2

macca-uk Author

Level 1

8 points

Oct 10, 2016 1:51 PM in response to think.different

Yeah, I'm rebooting into recovery mode. Do I need to do anything about the 'OS X Base System', or can I just format the drive and not worry about it?

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Answer 3

Oct 10, 2016 2:05 PM in response to macca-uk

I believe OS X Base System is the a part of the recovery disk. I'd leave alone.

There is a good explanation here:

Let me start at the beginning: your hard drive (/dev/disk0) has two relevant partitions: Macintosh HD (your regular startup volume), and Recovery HD.

Recovery HD is marked in the partition table with the type Apple_Boot, but is actually in the normal HFS+ format. It contains minimal booter files and kernel, and at /com.apple.recovery.boot/BaseSystem.dmg, a disk image with a stripped-down and tweaked copy of OS X. The booter mounts this volume (it attaches as /dev/disk1), and transfers to OS X running on it. This is the Mac OS X Base System. Notice that the Recovery HD is only 650MB, but Mac OS X Base System is 1.4GB? That's because it's a compressed disk image (and I'm pretty sure that compression is the reason they bother with all this disk image trickery). Actually, BaseSystem.dmg is compressed down to only 451MB (at least in OS X v10.7.0). Also, the volume naming is somewhat inconsistent. You've got /dev/disk1s3 named "Recovery HD", but for some reason it's mounted as "/Volumes/Image Volume" in recovery mode. BaseSystem.dmg has a volume named "Mac OS X Base System".

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