Re: RE: Fragmentation
"The difference is that this doesn't impact on the performance. "
True, but the block erase issue is the "new fragmentation", and can impact performance. For the original poster's benefit, SSD's can write data to an 4k "page", but can only erase a block of pages of around 512k. It has to erase blocks because it can only write to erased pages (unlike an HDD that can overwrite existing data). Like an HDD deleting or moving a file or page of data on an SSD only moves the file - it doesn't erase the old data, which still sits around until it is erased by the drives firmware, or the issue of a TRIM command by the OS. If there's sufficient free or erased space when you command a write, then you see no problem, but as soon as the SSD has to start moving pages around and erasing blocks before it can write then it is like swimming in treacle.
If you're lucky with your hardware and OS, and TRIM commands are issued silently and you'll never know (or need to know) what's going on under the bonnet. Also if the SSD's "garbage collection" works adequately then you'd probably never come across the problem. But if you're using the SSD as a system and data drive, then anybody whose activity involves big file copies (like video edits) and takes up a large amount of the SSD capacity may be at risk of this occuring because you run out of free or erased space. TRIM will stop that. The same can happen with a lot of smaller file writes, but most of us won't fill a large drive with small files.
If the garbage collection routines are good then (perversely enough) a few big file writes and deletes will fix the problem, albeit you have to wait for them to complete. Plenty more of this if you search the web, but just a personal suggestion that you don't plan to fill the bulk of the SSD unless you're sure that TRIM will work.
Retrofit SSD's are at particular risk of being installed on systems that may not be TRIM compatible either because the OS doesn't support it, because they've got older hard drive controllers that don't pass the command from the OS, or other hardware incompatibilities.
If all that sounds off-putting, don't let it. My home machine runs off a 230 GB SSD, and it is excellent - things just happen instantly. But I've got a separate HDD for my large FLAC music collection, for videos and such like. Eventually the photo collection may have to migrate to the HDD, but at the moment I have space to spare.