theterminator93 wrote:I have a Crucial M550 240 in my T420; I just installed a Samsung 850 250GB in a friend's T420.
I think the Crucial MX200 is the competitor to that and is about the same price.
vivaelt42 wrote:Thanks.

The Samsung 850 2.5" SATA SSD has really good reviews on Amazon. I
I don't give weight to most buyer "reviews" on Amazon, unless there is a common complaint about DOA. I think you can do better by reading the professional reviews and the experience of enthusiasts on forums.
The Samsung 850 comes in two flavors - EVO and PRO. The EVO is TLC NAND, which enthusiasts feel should be avoided because TLC is unreliable. The EVO, at least in its previous model 840, eventually failed spectacularly as reads slowed to a crawl over time, and samsung was unable to fix it other than temporarily. On the plus side, the 850 EVO is about the cheapest SSD you can buy now. The 256GB EVO was recently C$79 which is US$56.
The 850 PRO is about twice as expensive but benefits from the use of MLC NAND at a glorious 40nm, and this drive benchmarks the fastest of any consumer SSD, at least in synthetic tests, but its 3D V-Nand is an untested technology. It looks promising, but buying new technology from Samsung is a risky proposition because Samsung seems to use customers as beta testers. And samsung support is infamous for being the worst in the industry.
The MX200 is priced between the two Samsung models and sports Micron's own well-regarded MLC NAND, in a small 16nm (smaller means hotter, slower and less reliable). Among the three drives above, this might be the best value for quality. It is abit slower and it has a nasty performance issue if you fill up the drive, but I think that can be avoided by heavily over-provisioning. In general, the difference in real-world performance among different SSD's is barely perceptible to most users, certainly for the typical user like on a T420, as T420 users presumably aren't power users who are heavily into video editing or CAD.
No matter which SSD you choose, it's recommended you over-privision it by leaving 20-30% of the total drive unallocated. This will help the performance and reliability. For the MX200, I'd go with at least 30% (tom's hardware recommends 50% I think) So you should partition your SSD with no more than 180GB (preferably less) of the 256GB total.
When reading about drives, don't confuse endurance with reliability. These are not the same by any stretch. Endurance is easy to ascertain; reliability is very difficult to assess and not really known until many drives have been used for a long time. I'm struggling to figure out which SSD sold today is a reliable drive. Just because an old Intel or Crucial has been reliable in the past does not mean the new model will be reliable - especially as they shrink cell size and/or change controllers.
I currently own an 850 EVO, Sandisk Extreme Pro, an Intel 535 and an unopened 850 PRO that I might return. I had an MX200 but I exchanged it unopened for the Sandisk Extreme Pro. All of these companies have generally good rep though none are perfect.
The Sandisk Extreme Pro has been out for >1.5 years so it has a track record now, and it has had a good rep for consistency and reliability, although lately I've read a couple of people who claim theirs died and so did their warrenty replacement. Lately the Sandisk Extreme Pro has sold for a great price - same as the MX200 - so I went for the Sandisk as it's considered a premium SSD. Tom's Hardware rates Sandisk Extreme Pro as the best performing SATA SSD as of November 2015 - and the 850 EVO as the best low-budget SSD.
See
http://www.tomshardware.com/reviews/ssd ... ,3269.html
But strangely and sadly, among all the drives mentioned above, only the Sandisk isn't self encrypting.
I recently realized that OCZ has, by far, the best SSD warranty support nowadays (simply enter your serial# online and OCZ sends you a replacement). And OCZ reliability seems to have improved from its bad SSD's of days past - which is good to see because back in the early 2000's I really liked OCZ memory & OCZ's Rally2 USB-flash drives.
I'd be very interested in hearing about the reliability of specific SSD models. I think your M550 was supposedly reliable, but again, that's no guarantee about the reliabilty of the MX200 because it has different size NAND cell, circuitry, probably a different controller and might be built in a different plant/country than before.