So you have a budget SSD, something like the Kingston A400, and half way through a multi gigabyte file it slows down !
Coming to think about it, this SSD does not have a DRAM cache, and should be slower but more consistent, right ? after all, you can’t run out of cache when there is no cache !
The answer is NO, just because it does not have RAM cache or even actual SLC flash, does not mean it is writing casually to its MLC flash, the controller uses trickery to speed up writing and sometimes reading
Most drives with no RAM cache (Examples below) use a method called Single Level Cell mode cache, but even this name is misleading, your cheap hard drive does not have “Single Level Cell flash memory” inside of it, Instead, it utilizes it’s own MLC by writing single entries to it (One bit of a multi level cell), then re-copying it the normal way
When you are copying a large file to the disk, all the blank space at that level has been consumed, and the disk is now writing directly to the 3 dimensional MLC flash, which is, in most cases, slower than a mechanical hard drive for sequential write !
The most common of such a controller is the Phison PS3111-S11-13, it is a relatively good controller if your purpose does not require super fast SSDs, the controller has some cool features including Bad Block management (Spare flash that automatically replaces bad cells), besides standard features like S.M.A.R.T., It also supports native command queuing (NCQ), EEC error correction, so all in all, this post is not advice to stay away, this post is just hee to explain that it will be slow
Examples of such disks:
Kingston A400
– 240GB = Phison PS3111-S11-13
Silicon Power A55
– 1TB = Phison PS3111-S11-13
HIJVISION C100
– 120GB = MAS0902. (Read features below), and while the controller seems okay, at least on paper, I can not seem to be able to figure out the 64GB x 2 chips that read (TZA512G221 060422JC JWT5220364RB)
The Maxio MAS0902 SATA DRAMless controller. comparable to the (Phison PS3111) but has some interesting tech upgrades, 1- AgileECC 2 (2nd gen ECC) 2- WriteBooster 2 (2nd gen SLC write buffer), DEVSLP (low-power mode), power and thermal throttling, and end-to-end data protection. The controller also supports both TCG-Opal 2.0 and Microsoft’s eDrive (IEEE1667) full disk data encryption.