I'm using a ThunderBay 4 external enclosure as my main storage and backup unit. Recently I bought two 1TB Samsung EVO 860 SSD to improve performance of my data drives. I installed them using NewerTech adaptors and formatted them in RAID 0 using Disk Utility RAID assistant. (I already tried with OWC RAID software with same results)

So I have:

  • The two first bays with the SSDs in RAID 0 (for data)
  • The following two with 2TB HD in RAID 0 (for backups)

The problem is that I'm getting write speeds of around 100MB/s on the data RAID when I should be getting around 800MB/s.

Read speeds are as expected, around 750MB/s.

Without RAID, the same happens, I get around 500MB/s read speed but only 100MB/s write speeds.

Any idea of what could be causing this?

UPDATE: After trying with all available chunk sizes (from 32k to 256k) for the RAID, still getting the same results.

Extra inforamtion

  • Using 15" MacBookPro13,3 (2016)
  • MacOS Mojave 10.14.1
  • Measured with both BlackMagic Disk speed test and iStatus menus.
  • Drives firmware revision: RVT01B6Q
  • 1
    Firstly check the firmware. Also manually run trim on them. Dec 6, 2018 at 10:47
  • I updated the post to reflect the firmware version, I doesn't look that there is an update on Samsung website. Now I'm trying to find how to run trim in an external drive
    – Pablo L
    Dec 6, 2018 at 11:23
  • Actually I only know how to update the firmware using Samsung Magician... Dec 6, 2018 at 12:41
  • @PabloLorenzo - Depending on the controller, it might not support TRIM, have you contacted the manufacturer for assistance?
    – Ramhound
    Dec 6, 2018 at 19:09
  • 1
    Do both RAID volumes behave the same? I assume without the new SSDs you got the high writing speed? I assume the HDs/SSDs in use are SATA? Can you attach them directly to a e/SATA controller an measure the MB/s (without the raid or any other interface in between)?
    – Albin
    Dec 12, 2018 at 15:03

1 Answer 1


After many experimentation I finally tried removing the adaptors, attaching the SSDs directly to the SATA interface and creating the RAID again.

It works fine, I'm getting the expected ~800MB/s read and writes speeds.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .