I’m currently running two 4tb HDDs in a DAS attached to a Lenovo Thinkcentre tiny. It’s more than enough for my usecase. (I don’t run Immich, but do run PhotoPrism, which is similar in terms of resource usage.) The DAS is attached to the Thinkcentre by USB 3.0 (you can do eSATA but I’m currently happy with this setup.) The HDDs are in a mirrored VDEV which is part of a ZFS pool. It’s running in on AlmaLinux with zfsonlinux.
I’m currently running two 4tb HDDs in a DAS attached to a Lenovo Thinkcentre tiny. It’s more than enough for my usecase. (I don’t run Immich, but do run PhotoPrism, which is similar in terms of resource usage.) The DAS is attached to the Thinkcentre by USB 3.0 (you can do eSATA but I’m currently happy with this setup.) The HDDs are in a mirrored VDEV which is part of a ZFS pool. It’s running in on AlmaLinux with zfsonlinux.