Adding second SSD to 2013 21.5" iMac

I assume you are aware of the difficulty of opening up the iMac?

What I would do is set up an external SSD via USB as my boot/applications drive and use the internal HDD for my storage needs.

 

The item you have shown from crucial is not compatible with your iMac, if you plugged in your unit info on the left hand side Crucial states it is not compatible.

Sorry not to sure which one would work, not to knowledgeable in the PCI area, hopefully someone else chimes in.

 

PCIe is NOT the same as mSATA. It physically won't mount.

That's why they don't endorse it.

There are PCIe SSDs in the wild, but in the M.2 NGFF form factor. Apple's PCIe SSDs have a custom form factor, so an M.2 PCIe SSD like the Samsung XP941 wouldn't fit.

 

No they are NOT physically identical. The contact heads are completely different.

 

[[ Oh yes, very aware of the difficulties involved, and may indeed go down the road of ordering a standard 2.5" SSD and putting it into a caddy ]]

My suggestion is that you add an external solution that DOES NOT require you to open the iMac. It will save you a lot of time and trouble.

You will lose LITTLE in the way of speed by choosing either a USB3 or thunderbolt "alternative".

You will lose next-to-nothing in the way of speed, and save considerable money, by picking the RIGHT USB3 external enclosure or dock instead of thunderbolt.

I recommend that you choose a USB3 enclosure or USB3/SATA docking station that specifically states that it's "UASP" capable. UASP stands for "USB Attached SCSI Protocol" and it is literally "a world apart" from the older USB2 standard.

An enclosure that comes to mind:
http://oyendigital.com/hard-drives/store/U32-M.html

A USB3/SATA dock that comes to mind:
http://plugable.com/products/usb3-sata-u3

 

Your best bet would have been SSD from Apple and external HDD for storage or a Fusion Drive. Seems like you've made things hard on yourself.

 

Well maybe before you made the purchase, you should've done your research and know that the 21.5" iMac isn't upgradeable post purchase (except the RAM, which requires a lot of effort to open it up).