El-Capitan has set my external HDD, which is formatted HFS+ to read only file system

Question

I have a 1TB Lacie drive on a Firewire 800 interfaced to my iMac, running El-Capitan. The drive is used for data only and is where the /users/myname path points. As it is getting short on space, I purchased a second Lacie 3TB drive and daisy chained it to the first drive. All good, and formatted HFS+ using the Lacie supplied utility. I then re-booted and noticed my desktop and all its app's had disappeared. For some reason, OSX had pointed my /users/myname path to the new drive!!! So, I reset it to where it was, re-booted and then had problems in that although the apps had all re-appeared, nothing would execute and I had a persistent pop up telling my the Library was corrupt, enter password to repair (It didn't work). So, I disconnected the new drive and then went into recovery mode and used TimeMachine to reset to a time before I added the new drive. The persistent message has now stopped, but some of the apps will not work, so I ran a terminal window and noted an error message stating the file system (relating to my data drive) was read-only. I ran Diskutil/first aid and it did not help.

Not sure why this has happened, question is - how do I fix it please?

Answer 1

Sometimes OS X will mount a device as read only when the filesystem is corrupted. To fix this, you will have to see that the disk is not in use. I gather from your description that some other disk is your startup disk but you will also have to log out from the account which has its home on the 1 TB Drive. Then you can try and fix it with Disk Utility or a third party tool like Alsoft DiskWarrior. If you are lucky, that will take care of the problem. If not, Disk Utility may tell you that there are hardware problems with the drive and you need to copy files off of it while you still can. If so, I would copy everything to your new 3TB drive.

I have sometimes seen Firewire devices interfere with each other. This could cause interrupted writes to disk which can cause filesystem corruption. Journaling helps to recover from such problems but I don't know if the Lacie supplied utility would enable journaling or not. I would be inclined to use Apple Disk Utility to reformat the disk and make sure it's journaled.