Question Query regarding SSD cache and reading large files or collection of files

[Kippa]

This is a bit of noobie question, but I know that when you WRITE to an SSD if the cache fills up totally full the write speed can tank. I just want to know when I am READING from and SSD or NVME does the same thing happen? For example say I have an NMVE with 14gb of SLC cache, when I write more than 14gb I am aware that the writing speed will go a lot smaller. What I want to know is this true for reading? Or can you read at full speed all the time and cache isn't really effected?

 

[Billy Tallis]

Reading from TLC flash is a multi-step process, to figure out exactly which of the 8 voltage levels a memory cell has been programmed to. But from that, you get three times as much data as reading from a cell of SLC, so the overall sequential throughput of reading from TLC NAND tends to be comparable to reading data still in the SLC cache. It's a bigger difference for QLC, which is why some QLC drives tend to leave data in the SLC cache until they need to free up space, while basically all TLC drives will flush the SLC cache when they get a spare moment.

The advertised write speeds of consumer SSDs pretty much only apply to the SLC cache, but the advertised read speeds are attainable when accessing TLC blocks, provided you're working with a large enough queue depth.