Mount external HDD readOnly option I have the following problem: I used the optical bay to use a HDD in my mid 2010 13" Macbook Pro in addition to my SSD. It was working just fine until a few days ago, when it started to get "slower". VLC Player (on SSD) wasn't able to play videos on the HDD anymore, and when I tried to copy files from the HDD to the SSD it took ages (the speed was about 20 mb/m). Also it took a really long time to see what's in a folder when I opened it (but after 5-10 seconds I could at least see what files were in which folder).

My first question is: Is my HDD slowly dying? What could the problem be?

A friend was trying to help me repair it (he tried several things in the terminal and in safe mode - I do not remember all of it, but anyhow.. nothing worked). During this we unmounted the HDD and since then I am not able to mount it anymore.
When I try

diskutil mount /dev/disk1s2 


in the terminal it says

Volume on disk1s2 failed to mount If the volume is damaged, try the "readOnly" option


How can I try to mount it in readOnly mode?

diskutil mount readOnly /dev/disk1s2


doesn't work..

I would really appreciate it if you could help me. I have a lot of new photos and music on the HDD I have not backed up yet.
Enter in Terminal.app:

sudo asr adjust --target /dev/disk1s2 --settype "Apple_HFS"


and then try: 

diskutil mount readOnly /dev/disk1s2