By JFW


2012-04-13 13:58:44 8 Comments

Just thought of a concern on the MacBook Air. Flash drives / SSDs have limited read and write capacity, right?

How do I know when I am reaching that? I don't want my data to be corrupted.

Thanks in advance.

3 comments

@Allan 2017-07-06 15:31:36

Flash drives / SSDs have limited read and write capacity, right?

Yes, but it's a calculated value based on a number of factors including, but not limited to:

  • Duty cycle (how much the drive is being used)
  • What it's being used for (i.e. more writes than reads or vice versa)
  • The type of SSD SLC (Single-Level Cells, used in enterprise applications) or MLC (Multi-Level Cells, used in consumer applications).

When will an SSD fail?

According to this SNIA article, hard drives see a Mean Time Between Failure (MTBF) of 1 million hours, while SSDs show 2.1 million hours. SanDisk® further rates its Lightning SAS SSDs at 2.5 million hours MTBF. Thus, SSDs have more than twice the longevity than HDDs.1

They go on to further differentiate SSDs from HDDs...

SSDs are different in how they wear in comparison to hard drives. Due to the characteristics of NAND flash, SSDs have a finite lifetime dictated by the number of write operations known as program/erase (P/E) cycles NAND flash can endure. The objective of SSD endurance numbers is to capture this consumable nature of flash storage into a quantifiable number to provide end users guidance on the anticipated lifespan for the drive in operation.

Meaning: It's a best guess number. Your SSD is not going to stop functioning when it reaches that "theoretical" limit. Chances are, you are going to outstrip the capacity of the drive with data long before you reach its wear limit; you'll buy a bigger one before it fails.

Just for grins and giggles, I used Intel's SSD Endurance Calculator to estimate the life of an SSD being used for Virtualization with a 100% duty cycle (worst case scenario).

It gave me a life of just under 6 years having written 62 petabytes (62,800 TB).

enter image description here

To put that into perspective2, you would need to

  • record 213 years, 6 months of full HD video
  • take 24,000 digital photos per day for the rest of your life

TL;DR

Yes, there's a limit, but you needn't worry about it. You simply won't be able to perform enough read/write operations before you run out of capacity.

If you're concerned about data loss, you should be doing backups


1 SanDisk: Speeds, Feeds and Needs – Understanding SSD Endurance January 2015

2 Lifewire: Terabytes, Gigabytes, & Petabytes: How Big are They?

@latusaki 2012-04-13 14:05:35

From what I understand you don't need to worry about that. Those limits are just as indication and you won't be reaching those in years (at least with newer SSDs). If I remember right, my Crucial M4's lifespan is over 5 years under heavy daily use (like 40gb write per day).

@EmmEff 2012-04-13 14:08:56

Keep regular backups and don't worry about it.

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