regression with gmirror, Promise SATA and 7.0 ?

Hello,

I have tried to switch my home server from a 6.3-PRERELEASE to the latest 
7.0-BETA1.5-i386-disc1.iso.

I have loopback-mounted the iso and unarchived the base and kernel to a new 
gmirrored partition hosted on two "Seagate ST3250823AS" SATA disks connected 
via a "Promise PDC40518 SATA150" controller.

after rebooting to the new "current" gmirror partition, any disk access gives 
errors such as :
ad6: WARNING - READ_DMA UDMA ICRC error (retrying request) LBA=58616578
ad6: FAILURE - device detached
subdisk6: detached
ad6: detached
GEOM_MIRROR: Cannot write metadata on ad6s3 (device=gm0s3, error=6).
GEOM_MIRROR: Cannot update metadata on disk ad6s3 (error=6).
GEOM_MIRROR: Device gm0s4: provider ad6s4 disconnected.
GEOM_MIRROR: Device gm0s2: provider ad6s2 disconnected.
GEOM_MIRROR: Device gm0s1: provider ad6s1 disconnected.
ad10: WARNING - SETFEATURES SET TRANSFER MODE taskqueue timeout - completing 
request directly
ad10: WARNING - SETFEATURES SET TRANSFER MODE taskqueue timeout - completing 
request directly
ad10: WARNING - SETFEATURES ENABLE RCACHE taskqueue timeout - completing 
request directly
ad10: WARNING - SETFEATURES ENABLE WCACHE taskqueue timeout - completing 
request directly
ad10: WARNING - SET_MULTI taskqueue timeout - completing request directly
ad10: TIMEOUT - WRITE_DMA retrying (1 retry left) LBA=62894473
GEOM_MIRROR: Cannot update metadata on disk ad6s3 (error=6).
GEOM_MIRROR: Device gm0s3: provider ad6s3 disconnected.
g_vfs_done():mirror/gm0s3f[READ(offset=5429510144, length=65536)]error = 6
vnode_pager_getpages: I/O read error

The same ad6 and ad10 disks are presently used under 6.x without any (visbile) 
errors (and have been for more than one year).

Thus, it seems that the combination of this Promise controller and the SATA 
disks has issues (there was a thread about Promise controllers and ZFS, but 
with no clear conclusion).

	TfH

PS : I was also burnt by the forced conversion of gmirror metadata from v3 to 
v4, which makes it tricky to backtrack to 6.x, once a 7.x kernel + gmirror 
has been booted once.