TrueNAS - Slow SSD Sync writes with PLP Drives

Well I’m at my wits end. I’m building a storage server for ESXi virtualization and need sync writes to be quick, as this is a VERY write intensive work load. I purchased 12 Seagate 1200.2 800GB SSD’s which are SAS 12Gbit. Specs indicate a max of 850 sequential write, so I divided that in half for good measure. Literature says the have Power Loss Protection, so they should work pretty good as SLOG for ZFS in an all sync write situation with ESXi. However they are performing very poorly. Each drive maxes out at around 30MB/sec during sequential writes with 64KB block sizes. Just to test it isnt the source, i did a zfs set sync=disabled Pool and viola instant 10Gbit ingest rate no problem.
I’ve checked modepage 0x08 on the drives and found nothing obviously broken there.
It’s as if something is denying the drive use of its internal SSD cache, as I would see on consumer SSD’s without PLP.
The drives are connected to an LSI 2308 card, which connects to an expander back plane with 4 channels and then connects to the 12 SSD’s. The card is in IT mode with firmware version 20.
System has 96GB of memory and dual E5 2420v2’s, running TrueNAS 12U1 (12.2-p2 BSD version)

Anyone out there had this problem with enterprise SSD’s and ZFS?
Any thoughts are appreciated.

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