ZFS raidz1 redundancy

Hi. I'm running running an i386 -CURRENT built on October 2nd. I have a 
raidz1 pool consisting of seven 400-GiB PATA disks. ad4 and ad5 are part 
of the pool. This afternoon, the following happened:

Oct 11 19:05:27 exodus kernel: ad4: timeout waiting to issue command
Oct 11 19:05:27 exodus kernel: ad4: error issuing READ_DMA command
Oct 11 19:05:27 exodus root: ZFS: vdev I/O failure, zpool=home 
path=/dev/ad4 offset=70362711040 size=21504 error=5

The machine proceeded to panic after that, and when it rebooted, the 
following happened after a while:

Oct 11 19:11:40 exodus kernel: ad5: detached
Oct 11 19:11:40 exodus kernel: ad4: TIMEOUT - READ_DMA retrying (1 retry 
left) LBA=32

It crashed again half an hour after that, and when it came back up, ad4 
was no longer detected by the ATA controller. The output of "zpool 
status" is as follows:

  pool: home
 state: FAULTED
status: One or more devices could not be opened.  There are insufficient
        replicas for the pool to continue functioning.
action: Attach the missing device and online it using 'zpool online'.
   see: http://www.sun.com/msg/ZFS-8000-D3
 scrub: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        home        FAULTED      6     0     0  corrupted data
          raidz1    DEGRADED     6     0     0
            ad4     UNAVAIL      0     0     0  cannot open
            ad5     ONLINE       0     0     0
            ad10    ONLINE       0     0     0
            ad11    ONLINE       0     0     0
            ad8     ONLINE       0     0     0
            ad9     ONLINE       0     0     0
            ad6     ONLINE       0     0     0

Is it possible that the data on ad5, in the midst of the failured of 
ad4, has become inconsistent with the other members of the pool, and 
that I need to bring ad4 online (I'm fairly sure that it's a 
motherboard- or power-related issue and that the drive is OK) to be able 
to access the data on the pool?

-Boris