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Permission Issues with Time Machine, Drobo

post #1 of 7
Thread Starter 
I'm having permission issues with Time Machine. When it tries to backup to my Drobo, it gives me an error saying that the drive is read only. Usually after repairing permissions on main drive and rebooting, it'll work again, for a while. I'm using a PowerMac with 10.5.3.

I found this thread with something I want to try (from talksense101):

"Also, type the command "id" in terminal and make sure your user group is "staff". if that is fubared, go to system preferences and "users and groups" and right click on your portrait after authentication and you will get the advanced options menu. You can change your group id in there. the staff group id is usually 20. don't touch the UUID in there or the user account will lose access to the system."

I have 5 user accounts on the system. One account does list '20' as it's group user ID, while the other 4 all list the user ID (such as 501, 504, etc) as the group user ID. Should I change the group user ID to 20 on all accounts? What exactly does this mean and do, anyway? I checked a couple of other Macs I have, and they all had matching user and group IDs. Any danger of losing access to account when changing group user ID to 20?

Drobo's website knowledge base says to use Cocktail, which is what I'll try next if this doesn't work.
post #2 of 7
Thread Starter 
Thought I had this problem fixed, but it's back again.

I have used Cocktail, but can't see that it did anything.

I've erased and formatted the Drobo twice since the original occurrence back in June. The first time that seemed to fix everything, but not as lucky the second time. I have another backup (SuperDuper) on a different drive now, so it's no problem reformatting the Drobo again. I've only used the Drobo for Time Machine backup, SuperDuper backup, and backup of files from external USB drive from music server (Mac Mini based)).

When I look at permissions on the Drobo, it lists:

system - read & write
admin - read & write
everyone - read only

and above the list, it says I can only read. My account is admin. No listing for staff. I've verified and repaired permissions on my internal drive, then verified permissions on Drobo (won't let me repair, since read only I guess).

I think the problem is probably rooted in the group comments above, as no "staff" is listed on Drobo permissions.

Any insight you could give me is appreciated!
post #3 of 7
Late reply, but someone else may stumble upon this as well. I have the same issue. Time Machine cannot write to drobo because of some permissions issue. It happens whenever my iMac restarts and drobo automatically remounts. In order to fix this, I just unmount drobo, unplug the firewire 800, and then plug it back in to remount it. Works fine after that. I've spent too much time searching for a better fix for this. Luckily for me, I don't restart or turn my machine off that often. Waking up from sleep is fine, but it still happens when turning on from off. Haven't done much troubleshooting and don't care to, but would like an explanation or a real fix if its out there.
post #4 of 7
To save unplugging, you can try ejecting the drive, go into Disk Utility and mount it up again.

When the drive is mounted, does the Finder prevent you copying to the drive? If so does relaunching the Finder change anything?
post #5 of 7
Hi. I am having a heck of a time with my Drobo as well and I think I have narrowed it down to an issue with Time Machine backups. Drobo seems to work fine until Time Machine starts to backup. Part way through the backup the backup fails and I start to get ongoing, strange permission problems with the Drobo volumes. I loose my Aperture and iPhoto libraries although there not really gone, a restart of my Mac and the Drobo and the reappear.

Once, after disconnecting the USB to the Drobo, I examined the Volumes folder using terminal and saw that my Mac still thought the volumes were there. Probably some type of alias - I deleted them, and reconnected the Drobo. Things were better for a while, but issues have returned. I can't copy large files such as the iPhoto and Aperature libs to other mounted volumes without receiving the same Permission error and having the copy process just hang until I have to relaunch the finder.

All of this is making me very nervous about my Drobo.
post #6 of 7
Sounds like a Time Machine lockout, imo.
post #7 of 7
Originally Posted by Rokcet Scientist View Post

Sounds like a Time Machine lockout, imo.


I could not find the answer here or when I called. I also searched online for HOURS and HOURS to find this. Thought this would help others. It is a terminal command, but it's very simple and does not delete data. Read below. Entered the one line command. Entered admin password and It was unlocked and ready to use.


Open Terminal and type in this command.

sudo chflags nouchg /Volumes/DROBO; sudo chmod 775 /Volumes/DROBO

Replace the name of the Drobo in place of DROBO above.
Add Quotes around it if there is a space in the Drobo name such as below.

sudo chflags nouchg "/Volumes/Drobo 16TB"; sudo chmod 775 "/Volumes/Drobo 16TB"

Here is an explanation of what the two commands that AGENTX gave you actually do:

sudo gives you temporary root privileges.
chflags lets you manipulate file flags. In your case, you have the uchg flag set on the DROBO volume. uchg is the user immutable flag, in other words it is allowed to be set by ordinary users for files and directories that they own, and it signals that this file or directory should not be allowed to be changed.
nouchg tells chflags to unset the uchg flag.
/Volumes/DROBO tells chflags where to unset the uchg flag. In your case, it is the top level of your DROBO drive.

sudo again, it gives you temporary root privileges
chmod is the command to change file modes and ACLs. "File modes" is just a fancy Unix way of saying the permissions on a file or directory.
775 is just a shortened way (the explanation of how to shorten file modes is a little more advanced, so just trust me on this one) that the file or directory's owner can read, write, and execute, the group owner can also read, write, and execute, and other users (anybody else) can read and execute, but cannot write to it.
/Volumes/DROBO again tells chmod where to change the file mode.

As you can see, the commands are changing permissions and file flags, but do not have any effect on data.
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