Skip SSD part of Fusion drive on Yosemite reinstall

[mailboxbetacoin]

My iMac is suddenly running extremely slow, to the point that apps are timing out when opening, nothing is working pretty much.
After trying the usual suspects (SMC, PRAM, disk permissions...) with no improvement (even got worse),I tried running diagnostics and reinstall from the recovery menu, but those time out too with nothing to try...
Next step is to to try reinstalling Yosemite from a USB drive; one thing that could be a problem is the hard drive, and since I have a fusion drive, I suspect the SSD part of the drive could be the issue as the system takes forever to boot, etc...
When reinstalling, is there a way to skip the SSD part of the fusion drive and only use the HDD?

 

[chrfr]

I suspect the SSD part of the drive could be the issue as the system takes forever to boot, etc..

I'd be more likely to suspect that the spinning disk part is having an issue but it's unlikely that is the real problem. When SSDs fail, they don't get slower, they just stop working.
Did you do a format and clean reinstall, or just reinstall the OS over the top of your existing installation?

 

[simonsi]

My iMac is suddenly running extremely slow, to the point that apps are timing out when opening, nothing is working pretty much.
After trying the usual suspects (SMC, PRAM, disk permissions...) with no improvement (even got worse),I tried running diagnostics and reinstall from the recovery menu, but those time out too with nothing to try...
Next step is to to try reinstalling Yosemite from a USB drive; one thing that could be a problem is the hard drive, and since I have a fusion drive, I suspect the SSD part of the drive could be the issue as the system takes forever to boot, etc...
When reinstalling, is there a way to skip the SSD part of the fusion drive and only use the HDD?

What fusion drive do you have?