What you DIDN'T know about SSDs (Part 1) - Can performance degrade over time?

Can SSDs slow down over time - more specifically, will write performance degrade? How do SSDs write data in the first place? What is TRIM, and why is it needed? Why is access time more important than throughput?

In the first episode of my new series, I explain and answer speed-related questions about solid state drives.

--
Hey, if you enjoyed this video - and can't wait for part 2! - please subscribe to my channel, HandyAndy Tech Tips.
--

My notes on this topic:
- Storage is, undoubtedly, the single largest bottleneck in modern PCs - no other upgrade, including changing your CPU, graphics, RAM, etc, will produce a bigger difference.

- The variable of "speed" can be measured in several ways. One of the main ones seems to be throutput - that is, how fast contiguous blocks of data can be transferred from disk to RAM. However, when using a drive in practice, your operating system will be manipulating data that has been scattered across the disk in multiple blocks. Seek time is thus very important.

- For a desktop hard drive, "access time" comprises both seek time (physical head movement) and I/O time (speed for an instruction to be sent to retrieve or write a file). The average seek for desktop drives is 9ms, rising to a maximum of 15ms for laptop or "mobile" disks. In contrast, the speed of SSDs is only dependent on I/O (no moving parts), and averages 100 microseconds. That's 0.1 millisecond.

- So SSDs are a lot faster than mechanical HDDs when it comes to finding non-sequential data. But when it comes to writing data, un-optimised SSDs may actually slow down over time. To fix this, your operating system must support a command called TRIM.

- NAND flash memory - as used in SSDs - is laid out in pages. Each page consists of many individual memory cells, and many pages make a block. The problem is that, while data can be written to each page - which is like a sector in a hard disk drive - it can't be erased from individual pages. Instead, an entire block
must be erased. What happens if you want to erase the data from one page, but keep the data in another? Well, you need to copy the data from the page into another block, then erase the entire original block.

- To stop this entire deletion and rewriting process from happening every time you want to store new data, a command called TRIM is used. This essentially deletes the old data after your operating system marks it as deleted - instead of just leaving it around, only to be cleaned up when you want to write new data.

Видео What you DIDN'T know about SSDs (Part 1) - Can performance degrade over time? канала HandyAndy Tech Tips