Comment by marcan_42
4 years ago
Apple do not have PLP on their desktop machines (at least not the Mac Mini). I've tested over 5 seconds of written but not FLUSHed data loss, and confirmed via hypervisor tracing that macOS doesn't do anything when you yank power. It just dies.
With truly no PLP I'd expect unrecovarable drives that have screwed up their FTL when you pull power.
You can design your FTL to be resilient to arbitrary power loss, as long as the NAND chips don't physically go off corrupting unrelated data on power down. That only requires extremely minimal capacitance. I believe Apple SSDs do have some of that in the NAND PMIC next to the storage chips themselves; it probably knows to detect falling voltage rails and trigger a stop of all writes to avoid any actual corruption due to out-of-spec voltages.
I've absolutely heard storage vendors talking about protecting just the FTL during power loss as PLP. You could have an FTL where any writes are atomic, but that gets in the way of throughput practically. The storage vendors don't seem to generally be on board that tradeoff except for 'industrial' branded SKUs that also make throughput tradeoffs anyway.
2 replies →