Option to trim (discard)

[ijackson]

Once a a device has been successfully verified with vbig, it is a good idea to "trim" it: that is, tell the SSD it no longer needs to store the verification data. This will improve the performance and lifetime of the device.

Doing this with an option to vbig would be more convenient and less risky than doing it another way: vbig knows precisely what it has just overwritten and knows that it can safely be discarded.

blkdiscard(1) knows how to make the relevant syscall. vbig could call it or make the syscall itself.

[ijackson]

(Recently I commissioned some new SSDs and forgot to do the trim at the time. When I did it later I chose to use LVM (with devices/issue_discards = 1), since LVM is pretty bulletproof and thereby can help avoid mistakes.)

[ewxrjk]

This seems like a good idea. It should be testable using the 'fakestick' nbd driver, since struct nbdkit_plugin has a trim method. https://www.libguestfs.org/nbdkit-plugin.3.html