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The write cache sprint
CONSUMER-GRADE SOLID–STATE DRIVES
(SSDs), including those Apple fits inside Macs, have a limited capacity to write data at full speed. That’s set by the size of their SLC (single level cell) write cache, as once that’s filled, speed drops to about a third. This writes single bits to memory cells in the SSD, instead of multiple bits.
A 2TB SSD has a cache of 50–150GB, so full–speed writing is only possible for a limited time. The faster the SSD, the quicker you can fill its cache. In the latest Thunderbolt 5 drives, that could be as brief as 10 seconds.
Once it’s full, the SSD needs a few minutes break to empty its cache and resume writing at full speed. Although this is only likely to affect videographers and others who need to write huge amounts of data at speeds over 2GB/sec, it’s still worth bearing in mind.