> The issue is not speed, its the USB disks. firstly you are reliant on the disks presenting themselves in the same order at the same time. (historically that w

> The issue is not speed, its the USB disks. firstly you are reliant on the disks presenting themselves in the same order at the same time. (historically that was challenging) ZFS can cope with this quite well, MDADM, not so much. I have checked about that and mdadm uses uuids to identify partitions on USB disks: https://serverfault.com/questions/739580/mdadm-can-i-reconnect-a-usb-disk-as-sata-without-needing-a-rebuild https://serverfault.com/questions/739580/mdadm-can-i-reconne... https://serverfault.com/questions/460138/mdadm-disk-configuration-by-uuid https://serverfault.com/questions/460138/mdadm-disk-configur... https://www.linuxquestions.org/questions/linux-software-2/mdadm-usb-drives-and-uuid-questions-4175530170/ https://www.linuxquestions.org/questions/linux-software-2/md... Here is how it looks on my array: root@arau:~# mdadm --detail /dev/md1 /dev/md1: Version : 1.2 Creation Time : Thu Dec 10 08:56:22 2020 Raid Level : raid1 Array Size : 4821105600 (4597.76 GiB 4936.81 GB) Used Dev Size : 4821105600 (4597.76 GiB 4936.81 GB) Raid Devices : 2 Total Devices : 2 Persistence : Superblock is persistent Intent Bitmap : Internal Update Time : Thu Apr 15 11:18:54 2021 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Consistency Policy : bitmap Name : arau2:1 UUID : 7c1e57ea:1f7ebff2:415c1b0a:8f959031 Events : 21463 Number Major Minor RaidDevice State 0 8 2 0 active sync /dev/sda2 1 8 18 1 active sync /dev/sdb2 root@arau:~# root@arau:~# mdadm --examine /dev/sda2 /dev/sda2: Magic : a92b4efc Version : 1.2 Feature Map : 0x1 Array UUID : 7c1e57ea:1f7ebff2:415c1b0a:8f959031 Name : arau2:1 Creation Time : Thu Dec 10 08:56:22 2020 Raid Level : raid1 Raid Devices : 2 Avail Dev Size : 9642249512 (4597.78 GiB 4936.83 GB) Array Size : 4821105600 (4597.76 GiB 4936.81 GB) Used Dev Size : 9642211200 (4597.76 GiB 4936.81 GB) Data Offset : 264192 sectors Super Offset : 8 sectors Unused Space : before=264112 sectors, after=38312 sectors State : clean Device UUID : 52594d2c:77f9c0cc:0b4243f6:6a8e6bcb Internal Bitmap : 8 sectors from superblock Update Time : Thu Apr 15 11:18:54 2021 Bad Block Log : 512 entries available at offset 32 sectors Checksum : ca81c1ad - correct Events : 21463 Device Role : Active device 0 Array State : AA ('A' == active, '.' == missing, 'R' == replacing) root@arau:~# You see the second UUID entry? It is an USB disk. And I looked into the madm changelog and git log and I did not find any reference to problems as you describe since 2014. I am a bit confused why you refer to hypothetical problems or ones which do not exist anymore for years?