https://jira.ixsystems.com/browse/NAS-108881
Turns out, there’s a change that happened in TrueNAS 12.0-U1.1. It bit me, and I lost some data 
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As of this posting, I don’t have time to test the thing suggested in the issue (I filed an issue that was marked as duplicate,) but I plan on trying it out next weekend.
I thought I’d post this here, in case any of ya’ll have the popular LSI 2008 HBA. It’s been mentioned that it has problems with Seagate drives, but I haven’t personally had these problems. It’s been rock solid for years, until yesterday.
To describe the problem, I had drives constantly detaching and reattaching from the controller.
stuff looked like this in the logs:
mps0: IOC Fault 0x40000d04, Resetting
mps0: Reinitializing controller
mps0: Firmware: 20.00.04.00, Driver: 21.02.00.00-fbsd
mps0: IOCCapabilities: 1285c<ScsiTaskFull,DiagTrace,SnapBuf,EEDP,TransRetry,EventReplay,HostDisc>
(da9:mps0:0:17:0): Invalidating pack
da9 at mps0 bus 0 scbus0 target 17 lun 0
da9: <ATA WDC WD2001FFSX-6 0A81> s/n WD-WMC5C0D6YZ1L detached
mps0: Error reading device 0xd SATA PASSTHRU; iocstatus= 0x47
mps0: Error reading device 0xd SATA PASSTHRU; iocstatus= 0x804b
mps0: Sleeping 3 seconds after SATA ID error to wait for spinup
Just thought I’d post here, because it was very frustrating for me to figure out, and I’m hoping to save ya’ll some time.