One trick to keep SSDs working efficiently when TRIM is not an option is to leave between 8-12 % of the drive unformatted. This gives the controller room to shuffle 'used' blocks out of service, prior to deleting them and marking them as ready for re-use.
This is mainly due to the nature of flash memory, and the way in which it works. A traditional hard drive, the instant a piece of data is deleted, will straight away report to the host system that that location is ready to be re-used. With flash, it's all down to the way in which blocks of memory (not the individual cells) are deleted, before they are able to be re-used. In other words,
1) With a hard drive, any given data location can be over written immediately.
2) With an SSD, even if a given 'block' is only half-full, say, the
entire block has to be deleted, then marked as 'ready for re-use' before it
can be used again.
Hope that clarifies matters a wee bit.
Mike.
