TLC vs MLC vs SLC, Performance, benchmarks and reliability.

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TLC vs MLC vs SLC, Performance, benchmarks and reliability.

SLC, Single Level Cell (1 bit)

  • Generally 100000 write erase cycles
  • Erase time: 1-2.5ms

MLC, Multilevel Cell (2 or more bits)

  • Anywhere from 3000 to 15000 write erase cycles
  • Erase time: 2.5-3.5ms

TLC, Triple Level Cell (3 bits)

  • Anywhere from 1000 to 5000 write/erase cycles
  • Erase time: 4-5ms

 

Currently TLC offers the best performance/reliability per $ due to the fact that its the cheapest software and reliability has been improved exponentially over the past few years. MLC is also fairly close in performance/reliability per $, overall a MLC 2 bit cell has about 3x more write/erase cycles than a 3 bit cell so enterprise products tend to be MLC or SLC as SLC does have the best overall reliability with generally is well over 100,000 write/erase cycles ten times that of a MLC unit without software optimizations. Since software can be used to improve the overall reliability issues things can get quite complicated.

First thing to consider is amount of data you will be writing to the drive each day and how long you need the drive to last as SSD drives will all fail at some point based on number of write/erase cycles to the drive.

If the data is static, meaning very little writing/erasing to the drive then go with TLC,

If you plan to have moderate to heavy data writes/rewites/erasing then MLC or SLC, for example mail or database server.

With standard 3x Write Amplification* and 20GB a day in new data writes a 128GB SLC drive should last about 5-6 years and a MLC drive should last about 17-18 years assuming nothing else with the drive fails before that. In a enterprise environment you might have 40GB/day and the lifespan would drop to 2.5-3 years on SLC or 8.5-9 years on a MLC disk.

Enterprise vs Consumer grade SSD's:

The real difference between consumer grade SSD and enterprise grade is how efficiently the drive handles data read/write/erase cycles and sometimes its just marketing so check the MTBF; this should be 1,000,000 at a minimum. Next you will want to check the IOPS(input/outputs per second); in most cases you should look for something with 80,000 or more for both read and write.

Note on SLC:

Because very few people need a drive to last longer than 5-10 years SLC has not had much development keeping the price high and size very small, this is why most people choose MLC or TLC SSD drives today. 

 

Write Amplification is when SSD cells are erased before being written, this is required. when data is written to the disk the flash controller updates the LBA with the location of the data/metadata any old data still remains on the disk and must be erased. Some drives can offer solutions to this by methods like over provisioning, allowing new data to be written next to the old data without fragmentation and erasing the old data improving performance and the life of the disk but lowering the capacity. Another method it to separate static and dynamic data sets reducing the erase cycles for content that is rarely changed allowing the firmware to be more efficient and rotate usage over the life of the drive. 

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