I want to change HDD in Hitachi SMS100

Hi to all,

I have a Hitachi Simple Modular Storage 100, it's EOL since 2013.

If I find the HDD right, how I can to replace it without loss the data in RAID6 hdd configuration?

If I open the webpage of SMS100 I see 12 hdd (4 hdd in warning.. perhaps broken), but I see only 10 hdd in front of server. Where are the other?

How do I know which hdd are dead? (there isn't numbers on hdd)

Thx (and sorry for my english)