gmirror help

I just started using gmirror and I'm booting from it. What strikes me 
odd is that there is some error messages in messages.log:

ad4: 35304MB <WDC WD360GD-00FNA0/35.06K35> [71730/16/63] at ata2-master 
SATA150
GEOM_MIRROR: Device mirror0 created (id=3031340501).
GEOM_MIRROR: Device mirror0: provider ad4 detected.
ad6: 35304MB <WDC WD360GD-00FNA0/35.06K35> [71730/16/63] at ata3-master 
SATA150
GEOM_MIRROR: Cannot add disk ad4s1 to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad4c to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad4f to mirror0 (error=17).
GEOM_MIRROR: Device mirror0: provider ad6 detected.
GEOM_MIRROR: Device mirror0: provider ad6 activated.
GEOM_MIRROR: Device mirror0: provider mirror/mirror0 launched.
GEOM_MIRROR: Device mirror0: rebuilding provider ad4.
GEOM_MIRROR: Cannot add disk ad6s1 to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad6c to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad6f to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad6s1c to mirror0 (error=17).
GEOM_MIRROR: Cannot add disk ad6s1f to mirror0 (error=17).
SMP: AP CPU #1 Launched!
Mounting root from ufs:/dev/mirror/mirror0s1a

and after booting the mirror is in DEGRADED mode:

# gmirror list
Geom name: mirror0
State: DEGRADED
Components: 2
Balance: load
Slice: 4096
Flags: NONE
SyncID: 1
ID: 3031340501
Providers:
1. Name: mirror/mirror0
    Mediasize: 37019565568 (34G)
    Sectorsize: 512
    Mode: r6w5e2
Consumers:
1. Name: ad4
    Mediasize: 37019566080 (34G)
    Sectorsize: 512
    Mode: r0w1e1
    State: SYNCHRONIZING
    Priority: 0
    Flags: DIRTY, SYNCHRONIZING
    SyncID: 1
    Synchronized: 9%
    ID: 2876396261
2. Name: ad6
    Mediasize: 37019566080 (34G)
    Sectorsize: 512
    Mode: r6w5e3
    State: ACTIVE
    Priority: 1
    Flags: DIRTY
    SyncID: 1
    ID: 881985206

Geom name: mirror0.sync
Consumers:
1. Name: mirror/mirror0
    Mediasize: 37019565568 (34G)
    Sectorsize: 512
    Mode: r1w0e0

I'm running FBSD 5.3-RC1 (just installed from cd) on dual-opteron (64b) 
tyan K8S Pro. Two 37G raptors as ad4 and ad6.

-- 
br,
Tommi