TRIM makes no guarantee that the data is actually cleared out. It's kind of a big deal for parity-based RAID. The next read could read zeros, all ones, the old data, or any old garbage.
But there is absolutely no reason to make a new command for this NOR is there any need for the controller to actually erase the data.
All you need to do is modify (if it doesn't already do that) the drive's firmware return all 0s if an OS tries to read an address whose current status is trimmed. Then you put a sticker on the box that says "RAID Compatible TRIM". Presto, problem solved.
The spec should have been amended to require this years ago. (as in, from the first TRIM drive)
But instead they are trying to milk companies for the "feature" (same way WD limits TLER... TLER is merely disabling a feature called Deep Error Recovery because it freaks out badly designed raid controllers).
The advantage of having it as a unique command means that if you connect a hypothetical older drive that returns garbage data to a new controller that sends TRIM to parity capable RAID then it will cause corrption. If the new controller does NOT issue TRIM commands, instead only issuing dtrim, then it will simply do nothing on such an older drive. No data loss, but no trim either (which is a shame).
The downside is you now need to add a new type of command at every point of the chain and older drives that have TRIM and return all 0s when a trimmed address is queried will not work without a firmware upgrade adding dtrim support (which is highly unlikely to happen).
What irks me (beyond the fact that this was not included in the original trim spec) is that this issue was raised and work began on dtrim early enough that it was simple enough to amend the TRIM specification to include this and then have a VERY short list of drives that were made pre amendment (and whose manufacturers refused to provide a firmware update)... short enough that you could test them all/ask the manufacturers what behavior they have and compile a complete list of under a dozen specific drive models to exclude and put that exclusion list in RAID controllers.
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