On Thu, 21 Feb 2019 22:01:24 -0500
"Martin K. Petersen" [off-list ref] wrote:

Consequently, many of the modern devices that claim to support discard
to make us software folks happy (or to satisfy a purchase order
requirements) complete the commands without doing anything at all.
We're simply wasting queue slots.

Any example of such devices? Let alone "many"? Where you would issue a
full-device blkdiscard, but then just read back old data.

I know only one model(PLEXTOR PX-512M6M) of dozens tested, which is peculiar
that it ignores trim specifically for the 1st sector of the entire disk. But
implying there are "many" which no-op it entirely, seems like imagining the
world already works like you would assume it to.

-- 
With respect,
Roman