Verify Blocks Being Marked For Reuse in FS

[dman777]

How could I verify that blocks are actually being marked for reuse in my filesystem?

[BradN]

Are you talking about TRIM support on SSD or just filesystem marking blocks freed in general?

If it's the former, make sure you're using a filesystem that supports TRIM, and check dmesg output from bootup and make sure the right things are showing up for hard drive controller support (sorry I haven't worked with TRIM so i'm not directly familiar)

If it's the latter, df should indicate more free blocks after doing a remove. The main cause for something not being freed after deletion is the file is still in use (linux differs from windows in that files can be deleted while still open by a program - it is immediately unlinked from the directory listing and the actual file delete occurs on close).

Another possibility for free space not being reclaimed is filesystem corruption. Particularly on FAT filesystems, it's very easy to get phantom space usage after file deletion if the device is removed before properly unmounting (the directory tree is updated with the file removal but the FAT isn't and the space is still allocated in there). Easiest way to fix is copying files off and reformatting, and moving files back on. If that isn't practical there's fsck.msdos that will probably dump those extra chains to recovered files which you can delete.

Good luck!