You said “quoting from Sandisk tech help”, therefore it’s not your opinion but their statement which you just mentioned. And my comment was about their statement. Apart from that one thing, which, as I want to emphasize, is SanDisk thesis, there’s nothing in your comment that can be thrown upon, especially a poo. As you can see, I’m a tech savvy, so I wouldn’t call bulls**t on anything that could be true, even partially.
Just to clarify - what you essentially did was a data-destructive way of performing “TRIM” command on the stick. Since those memories are practically an SSD with an USB port, they need to flag sectors that are ready-to-erase so a garbage collector will perform its work and prepare them for next write cycle. For some reason (firmware bug perhaps?) the controller didn’t do its work properly (or rather “at all”) and after you’ve written a dozen Gigs to the stick and deleted them now & then, all of the (free at the time) drive space was marked as ready-to-erase. Crippled garbage collector didn’t do anything about it, therefore every write that drive wanted to perform had to be preceded by an erase cycle, which changes the “write” operation to “read-erase-change-write”, where the deletion takes a ton of time, resulting in write speeds that are so poor that you’d consider dismantling one computer and plugging your drive to the other because moving data that way would still be faster than copying it through the stick that’s slower on writes than 10 Megs a second.
And since the safe erase did bring back the performance of your hardware, you can be more than sure that after some time you’ll be back in square one, because if the garbage collection doesn’t work, when you start to run out of free pages (and you eventually will), the write speed of stick will drastically decrease to a level of single-digit Megs per second.
Filesystem doesn’t have anything to do with it. Moreover - if somebody says that it’s due to the “FAT corruption”, then I’d like to ask one thing - what if one does have an NTFS file system? It doesn’t have a File Allocation Table. What if somebody did format the drive to, let’s say, EXT4? Or HFS+?
Same thing for sector sizes. It doesn’t really matter how big sector you decide to use. 512B? 4K? 16K? Or maybe 64K? It doesn’t matter, as long as the beginning of the drive starts at sector that’s a non-zero power of 2 OR exacly 0 to avoid misalignment between physical and logical structure of the drive.
Bearing that in mind, after you’ve done the secure erase, you’ve completely destroyed any structures that the manufacturer could have created (data offset would be one and only thing that could matter here, but since you didn’t format the drive later under SSD-unaware XP or W98, it’s not an issue), still you got your speed back, so it only confirms that the stick is faulty.
Replace it as soon as possible, because you’ll hit the wall sooner or later and since you’re running an OS on that, it’ll be a real pain to use a drive that’s as slow on the writes as an HDD that’s on PIO mode 1.