I have a 2011 iMac whose drive has failed but the data can be recovered per the Genius Bar at Apple. To retrieve data I want to use my old Mac Mini. I have a fire wire 400 connected to the Mac Mini (host) and a converter (800) plugged into the other end the iMac for Target Disk Mode (TDM). When I hold down the T key on the TDM the symbol comes up and is moving on the screen. When I start the Mac Mini, host, I do not see the TDM on the desk top. What are the steps I need to go through in order for the Host to recognize the TDM drive? Any help would be appreciated.
First off, it strikes me as odd that they would say the drive has failed but that data is recoverable. Did they mean the OS is corrupted, but the drive is physically intact?
The drive will only appear on the desktop if it is in a format that the Mac OS understands. I would launch Disk Utility, which sees a level deeper and will see a drive that is unformatted, etc. If you do see it listed in Disk Utility, I would select it and do a disk repair. Once done, it may appear on the desktop. You can also select it and choose "mount" to see if it can be mounted on the desktop. If none of this works, it may be too corrupted to be restored. There's a chance you can format it at this point, but while that may leave you with a working drive again, it will eliminate the possibility of getting your data. The thing to do at this point (drive showing in Disk Utility, but not mounting/appearing on desktop) would be to install and run a more advanced utility like Data Rescue, or even send it to a company that specializes in data recovery (although they will charge you $1000+). If the drive won't show up in Disk Utility at all, then it may be too far gone to recover.
Before taking drastic measures, I would definitely try the reverse of your current setup -- try booting the iMac from the drive in the Mini. Do this by putting the Mini in target mode, and then power on the iMac in option mode, by holding down the "option" key as you power on. Option mode shows you the available bootable volumes, and the Mini's hard drive should appear. Select it, and boot from it. You will then be using the iMac's hardware to boot from the drive in the Mini. The iMac's drive may or may not appear. If it does, you can copy data to the Mini's drive. If it doesn't, go into Disk Utility and follow the instructions as above. Just keep in mind that you're using the Mini's hard drive, so the iMac's drive in this scenario is not the active running OS (which can make things confusing).
I should also mention that I'm assuming the Mini has an Intel processor and is not a G4. This is important because an Intel iMac will not boot from a G4's hard drive, because G4s use a different drive format. Also, Macs will not boot from an OS that came before the time it was produced. So for example, if Snow Leopard was the OS that came with the iMac, but the Mini has Leopard, the iMac would then not be able to boot from Leopard. But if the Mini has Snow Leopard, and the iMac came with Snow Leopard, then that should be a match.
That's pretty much it. I would reset the PMU/SMC and PRAM on both computers, because sometimes the lack of doing that can cause a volume to not show up.
Anyway, good luck, and let me know how it goes!