Re:WD Passport 4TB drives don't support WRITE SAME command
by mehrdadn on Friday March 27, 2020 @03:12AM
(#22700927)
Is this just a theoretical thing, or have there been actual drives that lied about invalid opcodes on a read and then proceeded to destroy the drive if you issued a fallback read? I have a hard time believing a hard drive would behave like a C compiler if I'm being honest...
Re:WD Passport 4TB drives don't support WRITE SAME command
by zaarn on Friday March 27, 2020 @03:50AM
(#22701058)
As I mentioned earlier, there was a series of CDROM drives that upon receiving an unsupported command (and this was before you could discover it) would lead to all further data being interpreted as firmware data for an update and brick the device. If you issued a fallback read then the device would become bricked, if you reset the bus and reinitialized the device, everything was fine.
Discovery has of course improved this, so we know what a harddrive can and cannot do. Harddrives that lie about what they support shouldn't have the appropriate seals and trademarks of SATA or SAS on them, as they must be certified by those entities.
But it is much easier to rely on what is known to work instead of issuing potentially non-working commands to the point that there is no reason to have a fallback other than "rediscover what it supports".
I don't get why you would even want to use a fallback command on a drive that is in a potentially unknown or undefined state.
If discovery led to an invalid opcode the drive is faulty, end of story. The SAS and SATA standards are very clear on what is permitted and what is forbidden and that falls very far on the side of "not allowed".