iMac 27 mid 2010 - HD disappeared

Hello everyone, today I write for a "Mysterious Problem" ....

About 2 months ago I proceeded with the hardware upgrade my iMac 27 mid 2010 entering a Samsung SSD 250 while maintaining the internal HD 1Tb as secondary.

I proceeded with all guides iFixit etc., by inserting second cable sata etc ...

In these two months I used all enjoying the improvements and performance to date; until now because suddenly the secondary HD (or the original 1TB) disappeared.

I proceeded with the various software (Drive Genius - TechTool 8 - DriveWarrior etc.), at first I thought it was just skipped the partition map, but something still does not come back, with all the software analyzes the SMART status is intact, and yet despite this' and despite also using Disk Utility disk is now visible, reading and writing is dramatically blocked, less than 1Mega per second (Blackmagic disk), practically unusable, even during startup, the secondary appears with HD-minute delay .

I do not understand, for so many years this thing has ever happened to me, I not understand what could have happened, everything ran beautifully.

Does anyone have any idea what might have happened? HD is really dead? It may be the cable? I do not understand how suddenly such a thing could happen.

Thank you

Welcome to the forum! Your symptoms on the drive seem to indicate that yes, it has died, or is dying fast. What happens is that the drive is having to try multiple times to achieve a successful read or write, which makes it appear to be very, very slow. Disk Utility doesn't test for speed, just that a read/write is successful. The drive is at least 5-6 years old, which is pretty old for a spinner. Drives are crazy cheap right now, so I would recommend you get a replacement (and make backups NOW because that drive is going to die soon.