Raid0 rebuild slows to a crawl

[David Liontooth <lionteeth@cogweb.net>]

I'm trying to use a WD3200AAKX-001CA0 drive in a raid1 configuration 
(Debian squeeze mdadm 3.1.4-1+8efb9d1), but adding it is unusably slow:

# cat /proc/mdstat
Personalities : [raid1]
md1 : active raid1 sdb3[2] sda3[1]
       73015360 blocks [2/1] [_U]
       [>....................]  recovery =  0.0% (28928/73015360) 
finish=2521.6min speed=482K/sec

dmesg shows no errors:

md: recovery of RAID array md0
md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
md: using maximum available idle IO bandwidth (but not more than 200000 
KB/sec) for recovery.

The drive itself doesn't seem to have a problem, though it's not 
particularly fast:

# hdparm -tT /dev/sdb

/dev/sdb:
  Timing cached reads:   11220 MB in  2.00 seconds = 5614.03 MB/sec
  Timing buffered disk reads: 174 MB in  6.44 seconds =  27.01 MB/sec

# smartctl -a /dev/sdb

5 Reallocated_Sector_Ct   0x0033   133   133   140    Pre-fail  Always   
FAILING_NOW 1265

# hdparm -i /dev/sdb

/dev/sdb:

  Model=WDC WD3200AAKX-001CA0, FwRev=15.01H15, SerialNo=WD-WCAYUEJ66523
  Config={ HardSect NotMFM HdSw>15uSec SpinMotCtl Fixed DTR>5Mbs FmtGapReq }
  RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=50
  BuffType=unknown, BuffSize=16384kB, MaxMultSect=16, MultSect=off
  CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=625142448
  IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
  PIO modes:  pio0 pio3 pio4
  DMA modes:  mdma0 mdma1 mdma2
  UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6
  AdvancedPM=no WriteCache=enabled
  Drive conforms to: Unspecified:  ATA/ATAPI-1,2,3,4,5,6,7

  * signifies the current active mode

Is this a known problem? Only see it with this WD drive.

Cheers,
Dave