13" MBP from 2011, running Lion. HD has BootCamp parttion in addition to Mac parttion and now with Lion the Recovery HD.
Doing some routine maintenance today. In Disk Utility there has appeared another partition named "disk0s1". I am sure it wasn't there a month ago. DU shows it has capacity of 209.7 MB 195.5 available with 57 files Mac OS extended format.
What is this partition used for?
MacBook Pro, Mac OS X (10.7.3)
That is the Unix representation of your hard drive's first partition, the EFI partition. There's nothing that you do with that partition, so pretend it isn't there. It's used by the operating system.
Apparently you've enabled DU's ability to show invisible or hidden partitions such as this one and your Recovery HD partition. If so then these should appear ghosted.
Thanks for the prompt reply. I have turned off showing hidden partitions, the recovery HD (which was greyed out) is no longer visable, but the "disk0s1" still appears and is not greyed out whether DU is set to show hidden or not. I can verify disk etc. Only contains an invisble folder ".Trashes".
My iMac also running Lion has no such partition, which caused my confusion when one does have it and another machine does not.
Bill
PS the disk in question also appears on the desktop with the standard icon of an internal drive. I can even eject it. and keep on running.
Open DU with hidden partitions showing. Select the disk0s1 entry in the sidebar then click on the Unmount icon in the toolbar.
Now I feel really stupid. Been using Macs since 1989 (Mac SE). I went back to DU and looked at the drive in partition manager, and discovered I could delete the phantom partition without disturbing either the Mac or Boot Camp partition. Mac partion expanded by the amount of the one I deleted.
I was working under assumption I would need special disk SW or would need to do complete erase, restore, and taht is a big issue for me with the boot camp partition.
How my stupidity helps someone else.
Bill
Bill3 wrote:
discovered I could delete the phantom partition without disturbing either the Mac or Boot Camp partition. Mac partion expanded by the amount of the one I deleted.
Do not, repeat, DO NOT delete the EFI partition (disk0s1)!
Although not documented by Apple, it appears that, at least in some instances, the EFI partition is used by the EFI firmware update. The EFI firmware update may fail or refuse to install if the EFI partition is missing from a GPT-formatted disk. There may be other consequences, because the first partition on an Apple-formatted GPT disk > 2GB is always expected to be the EFI partition.
fane-_j:
Since I have already deleted it, what should I do now?
MBP does seem to start and run OK, however the bbot camp partition, while still visible, will not restart in Windows.
Bill3 wrote:
Since I have already deleted it, what should I do now?
I'm afraid I don't know, because you're using Lion. Otherwise, I'd say update your backups, re-format the disk, then restore from backup. But re-formatting the disk would destroy the Lion Recovery HD partition. I don't use Lion, so I can't advise you. Let's hope Kappy (you really should've heeded his advice to ignore it) or someone else who does use Lion can help.
the bbot camp partition, while still visible, will not restart in Windows.
I don't know if that's related or not. But you should also test if you can boot from the Lion Recovery HD partition.
What is "disk0s1"?
