Disk Utility: "Error: This disk doesn't contain an EFI system parti.. a RAID...
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Hello,
after installing refind 0.8.1, playing around with Linux Mint 17 MATE and uninstalling refind, I now get the following error message from Disk Utility when I select "Verify Disk" for the disk that both contains the Mac OS partition and also contained my Linux Mint partition before I deleted it:
"This disk doesn’t contain an EFI system partition. If you want to start up your computer with this disk or include it in a RAID set, back up your data and partition this disk."
To be precise, I installed refind 0.8.1, installed Linux Mint 17 MATE, tried but failed to create a new installation of MATE on the same partition, deleted the MATE partitions (including the Linux swap partition which seems to have been created by installing MATE). Afterwards I verified the disk and received the error message above. I hoped uninstalling refind would solve the problem but didn't.
Why does Disk Utility give me this error message? How can I solve this problem?
Last edit: Anonymous 2014-06-05
Here is my partition table for the disk:
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: Apple_HFS Mac OS 396.3 GB disk0s1
2: Apple_HFS Recovery HD 650.0 MB disk0s2
3: Apple_HFS Install OS X Mavericks 15.0 GB disk0s4
4: Apple_HFS Backup Storage 34.0 GB disk0s5
Considering the partition table, I change my question(s):
(1) Is the EFI system partition really missing or is there another explanation for this message?
(2a) If it IS missing, then what is the cause and how can I get it back?
(2b) If it is NOT missing, then why does Disk Utility give me this error message and how can I correct that?
After some more contemplation, I think I probably deleted it myself with MINT's Partition Manager (having booted it from a flash drive), thinking it is one of the MINT partitions I wanted to delete from the hard disk (the other two being the actual MINT partition MINT's swap partition).
Can I re-create an EFI system partition without re-installing Mac OS?
Yes, you can create a fresh ESP. My GPT fdisk (
gdisk) program will do this, although you'll need to usenewfs_msdos(I think that's the command name in OS X) to create a filesystem on it.Hello Roderick,
thank you for your reply. On the gdisk page, you state that it is "a powerful tool for experts". However, as you can imagine, I am not an expert and found the tutorial overwhelming. I would be grateful if you could be so kind and describe more specifically what I need to do.
If you can boot into Linux (even an emergency disk), you might find GParted easier to use: Create a FAT32 partition and then set its "boot flag." There's probably about 200MiB of free space at the start of the disk, which should work fine for this purpose.
So I only need to create a FAT32 with GParted, set its "boot flag" and that's it? There is nothing else I have to do and Mac OS automatically "knows" that this is the EFI partition?
That's right. An ESP is just a FAT partition with a particular type code set. GParted represents that type code as a "boot flag." (Note, however, that a GParted "boot flag" on an MBR disk is an entirely different thing.)
I did as you said (see screenshot), but Disk Utility still warns me that there is no EFI partition.
Why?
Does boot really mean EFI partition?
In Terminal.app, try these commands:
Output of the first command:
Output of the second command:
Looks like your EFI partition is disk0s8 (guid C12A7328-F81F-11D2-BA4B-00A0C93EC93B). An EFI partition usually has index 1 and label "EFI" in the GPT. Try a "diskutil list" to list the volume names (which may be different than the GPT label names).
Maybe try reordering the partitions with gdisk (gpt fdisk) and setting the GPT label of the EFI partition to "EFI".
Can I use GParted instead of gdisk to achieve the same? The latter seems cryptic to me.
In GParted, I set the EFI partition's label to "EFI". However, when I tried to apply this change, it got lost. In other words, the label was still missing afterwards.
Also, I couldn't figure out how to change the EFI partition's index to 1.
Last edit: Anonymous 2014-06-26
Changing the label in GParted will affect the filesystem's label, whereas
gdiskwill change the partition's label. The two are different data structures and can hold different (perhaps confusingly different) data.The ESP is in no way required to be on any particular partition or to have a particular label; it's simply a FAT32 partition with a partition type code of C12A7328-F81F-11D2-BA4B-00A0C93EC93B. The EFI spec (in which GPT is defined) is quite clear that it can reside anywhere on the disk, although putting it early on the disk reduces the risk of problems as the disk is used and partitions are created, deleted, and resized. If OS X's Disk Utility is enforcing some other rule, then it's not in compliance with the GPT spec. (Of course, this tool is from the same people who use the grossly non-compliant hybrid MBR, so this isn't really surprising.)
I think you should back up, though: Your first message reports what sounds like a warning message. (This is distinguished from an error message, which you called it, in that a warning doesn't stop you from doing something, but an error does.) If my understanding of your situation is correct, my recommendation is to ignore it; Disk Utility is just complaining about something that's perfectly valid, and mis-labelling it as something else. In other words, it's a (mostly) harmless Disk Utility bug, not an indication of a real problem on your computer.
If, OTOH, this is actually causing problems -- say, if Disk Utility won't make changes to the disk that only it can make -- then you'll need to work around it. Looking over your partition table, I'd say that the easiest way to do this is to create a new ESP in the 200MiB of free space at the start of your disk. You can do this in GParted by creating a FAT32 partition in that space and setting its "boot flag." This new ESP should be able to coexist with the first one; but if it creates new problems, you can copy anything you need from your current ESP and delete it.