Well, I gave up and went back to FreeBSD. However after a year and half, one of the disks in the ZFS mirror failed, and when replacing it I realized the pairing was not right (2009 vs. 2015 disks, 512 vs. 4k...), so the pool was likely to be rebuilt... so I thought "why not?" and got an additional disk, an AMD card, and finally built a sofraid raid1. The AMD card plays nicely too, being passively cooled (those Nvidia GTX 260 are powerful but too hot and noisy).
The disk with FreeBSD is carefully stored "just in case of accidents"
P.S.: ATI Radeon HD 5450