Noticed a performance hit "issue" this morning on MacPro 5,1 after the 10.13.2 (17C205) update when a system SSD (SATA) was connected directly to drive tray #1 via sled (OWC blue tray). SSD performance slowed close to 100MB/s for writes. Reads were unchanged. System drive was formatted (updated?) to APFS during the High Sierra update install by macOS. Swapped in an identical SSD (same brand/model/style, purchased at the same time) which was a system clone (Carbon Copy Cloner) and formatted HFS+ (Mac OS Extended Journaled). Speeds increased near where they were previously and within expected range. Put the original system SSD (APFS format) into a USB 3 enclosure. Performed a disk test and speeds checked very closed to where they should. Not scientific and speeds tested with AJA system test lite. Unsure if this is an issue with APFS & the security update when drives connected via SATA, or is this is/was something else. Reconfiguring SSD placements within the machine (some via PCI slot adapters) and drive performance is again as expected.