If you own a 2011 MacBook Pro and want to install a 2nd HD / SSD in the optical bay:
MCE's OptiBay Extreme
is on sale this week for $79 (regular $99). This is the only time of year I've seen it discounted. I've kept it in my bookmarks for the past 7.5 months, and this is the first time I've seen it on sale. Possibly only for this week - Cyber Monday week.
For those who do not know what this refers to. 2011 MBPs (early 2011 and late 2011) introduced 6G SATA connectors for both the HD bay and optical bay. But while the HD bay will take a 6G device, the optical bay came with a SATA 1.5 or 3.0 superdrive installed. Apple apparently never tested the optical bay with a device running at full 6G speed.
If you use a 6G drive in a 2011 optical bay, you get high error rates on the SATA bus, until the driver dismounts the drive. So if you use an OWC Data Doubler or regular OptiBay, you are limited to 3G devices. But 3G HDs/SSDs are uncommon today, and top out at 1 TB. 6G notebook drives top out at 2 TB today, with 3TB expected soonish. 5TB HDs are available in 15mm, so 3TB in 9.5mm could be announced any time. 4TB SSDs are available now for the price of a gold bar.
Apple subsequently fixed the 6G optical bay problem in the 2012 (non-Retina) models.
MCE examined the SATA signals, building a profile of what was going wrong. Then designed a mounting bay to cancel out the signal errors. I suspect the result isn't perfect, but any remaining errors are few enough for EC to fix. The driver does not dismount attached drives, and they run at full 6G speed.
So if you still use a 2011 MBP and want more / faster internal storage in the optical bay (anything bigger than 1TB) this is the solution. I wish it was cheaper, but it's the only game in town. Heads up to anyone interested - you can get it for a little less this week.