Samsung 840 EVO 250GB Review

Ok… So what is the deal with TLC? And no, it isn’t a Micheal Jackson reference.  Instead, TLC is what I consider to be a natural evolution in the SSD Market.  First, there was SLC, then MLC, and now TLC.  SLC, or Single-Level Cell can store 1 bit of data per cell.  Because of that, it costs much more per gigabyte but offers the highest performance.  MLC, Multi-Level Cell, is in the middle.  It can store 2 bits of data per cell and offers good performance and a decreased price point.  Drawbacks include a decrease in endurance and a far greater complexity in determining the drives state.  It is much easier to determine if an SLC is occupied.  TLC, Triple-Level Cell, is the most affordable of the lot.  However, it offers the lowest performance and an increased rate at which the NAND cells degrade.  With TLC there are 8 states to distinguish between, with only a few electrons making the difference between one state or another.

Samsung EVO 250 (25)

So, why would anyone want to buy an SSD with lower performance and an increase in cell degradation?  Well, engineers thought about it… a lot. They came up with complex and clever solutions.  With things like Advanced wear-level coding, new garbage collecting algorithms, improved ECC (Error-Correcting  Code), over-provisioning, and parallelization.

To get speeds up, manufacturers like Samsung, that make every single aspect of this drive, can choose from the highest quality NAND in their manufacturing process.  Also, the decrease in production costs for TLC means Samsung can increase the number of NAND chips in their SSD, which allows for more parallelization and the implementation of something called TurboWrite.

TurboWrite is a technology that simulates faster SLC NAND on a portion of the drive.  During write operations, data is first written to the buffer at accelerated speeds.  Then during the idle periods, the data is moved from the buffer to primary storage.

Samsung EVO 250 (26)

The buffer size varies with drive sizes and starts with a minimum size of 3GB on the 120GB flavor.

SSD Capacity 120GB 250GB 500GB 750GB 1TB
Buffer Size 3GB 3GB 6GB 9GB 12GB

Now, a buffer is just that… a buffer.  Under consecutive write operations, the buffer will fill. When that happens, the transfer will exit TurboWrite and write data directly to the drive at 3-bit MLC performance.

SSD Capacity 120GB 250GB 500GB 750GB 1TB
TurboWrite 410 MB/s 520 MB/s 520 MB/s 520 MB/s 520 MB/s
Exit TurboWrite 140 MB/s 270 MB/s 420 MB/s 420 MB/s 420 MB/s

About Joe D

I have always had a passion for everything computing. In early 2000, I decided to take my passion to the web. Thus, C.O.D. was born. Through the years we have made many great friends at C.O.D. and hope to continue our journey for years to come.

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