If these disks are in two logical drives of RAID 0, you may not have any recourse beyond copying your data off the system. 

You won't be able to just replace the failing disk without incurring data loss. 

Are you sure that you're using RAID 0?

Detect HP ML370 G5 Bad disk in RAID0
I've bought a chain wear checker made by BBB, but not sure what the percentage of worn is about?

It has 2 sides, one of them indicates that the chain is worn 75% and I should replace it in the near future. The other side shows, that the chain is 100% used and should replace it as soon as possible.

My detailed question :

What does these percentage mean? What is the equivalent of it in the metric system? 

Will 75% worn state affect my cogwheels also? Can I replace the chain to a new one without changing the drivetrain's other elements? 

I use a single-speed bike. Chain width is 1/8 inch. It consists 94 chain. (400km (250miles) / month)
