The life expectancy of SSD's
This post is to try and understand the life expectancy of SSD's.
The most informative information comes from Intel. The following references have been used to obtain other assumptions:
http://techreport.com/articles.x/15433
http://www.anandtech.com/cpuchipsets...spx?i=3403&p=4
Intel are quoted in these articles as stating that OEM's required them to prove that their SSD could provide 20GB writes per day for 5 years.
The variable factors on an SSD architecture are write amplification and wear levelling. (Cell construction is not considered and input on this would be welcome.)
Intel are quoted as stating that they use the following formula to calculate this.
Cycles = (Host writes) * (Write amplification factor) * (Wear levelling factor) / (Drive capacity)
Intel are quoted as claiming that other SSD manufactures use this formula:
Cycles = (Host writes) / (Drive capacity)
Based on a 32GB drive the difference between formula's give a variation of approximately 40%.
Using Intel's figures the life expectancy can be calculated as follows:
Intel formula based on 32 GB drive @ 20GB per day =
0.715 = (20) x (1.1) x (1.04)/ 32
0.715 cycles x 1,825 (5 years) = 1304.87
(Total life cycles) 10,000/ 0.715 cycles = 13,986 days or approx 38 years.
Drive will last approximately 38 years writing 20 GB per day
Intel formula based on 32 GB drive @ 100 GB per day =
3.575 = (100) x (1.1) x (1.04)/ 32
(Total life cycles) 10,000/ 3.575 cycles = 2,797 days or approx 7 years, 6 months
Drive will last approximately 7 1/2 years writing 100 GB per day
Intel formula based on 80 GB drive @ 20 GB per day =
0.286 = (20) x (1.1) x (1.04)/ 80
0.286 cycles x 1,825 (5 years) = 521
(Total life cycles) 10,000/ 0.286 cycles = 34,965 days or approx 95 years, 10 months
Drive will last approximately 95 years writing 20 GB per day
Intel formula based on 80 GB drive @ 100 GB per day =
1.43 = (100) x (1.1) x (1.04)/ 80
1.43 cycles x 1,825 (5 years) = 2,609.75
(Total life cycles) 10,000/ 1.43 cycles = 6,993 days or approx 19 years
Drive will last approximately 19 years writing 100 GB per day
Using Intel's formula and Intel's assumptions on other brands of "mediocre" quality" SSD's with a write-amplification factor of 10 and a wear-levelling efficiency factor of 5 (ref Tech Report) you get the following results:
32GB drive @ 20GB per day. Assume write amplification of 10 & wear levelling at 5
31.25 = (20) x (10) x (5)/ 32
31.25 cycles x 1,825 (5 years) = 57,031
(Total life cycles) 10,000/ 31.25 cycles = 320 days or approx 1 year
Drive will last approximately 320 days writing 20 GB per day
32GB drive @ 100GB per day. Assume write amplification of 10 & wear levelling at 5
156.25 = (100) x (10) x (5)/ 32
156.25 cycles x 1,825 (5 years) = 285,156
(Total life cycles) 10,000/ 155.25 cycles = 64 days
Drive will last approximately 64 days writing 100 GB per day
As can been seen the estimated life time is heavily dependent on the following factors if you assume 20GB writes per day:
• Size of the drive
• Write amplification factor
• Wear levelling
EDIT: Wear levelling:
Static wear leveling
This technique wear-levels over both dynamic and static data areas, so the entire capacity of the SSD can be used for wear leveling.
Reassigning static data is a more complex task than dynamic data because it requires multiple operations to safely move static data around. As a result, this implementation may impact the overall write performance.
Dynamic wear leveling
This technique only wear-levels over dynamic data areas. For example, an 30GB SSD with 20GB of dats only leaves the remaining 10GB capacity for wear leveling. Dynamic wear leveling has a shorter life expectancy compared to static wear leveling because only dynamic data areas can be used to rotate data, but write times improve.
