Same in Jaunty. Sata performance slow. Coping/moving data form root disk sda to others two sdb,sdc only 4-10MB. Moving data between sdb and sdc normal (50-70MB).

mindedie@mindedie-desktop:~$ uname -a
Linux mindedie-desktop 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64 GNU/Linux
mindedie@mindedie-desktop:~$ dmesg | head
[    0.000000] BIOS EBDA/lowmem at: 0009f000/0009f000
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Linux version 2.6.28-11-generic (buildd@crested) (gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4) ) #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 (Ubuntu 2.6.28-11.42-generic)
[    0.000000] Command line: root=UUID=82658bd4-0c50-4815-a528-9223cc582264 ro quiet splash 
[    0.000000] KERNEL supported cpus:
[    0.000000]   Intel GenuineIntel
[    0.000000]   AMD AuthenticAMD
[    0.000000]   Centaur CentaurHauls
[    0.000000] BIOS-provided physical RAM map:

 sudo hdparm -i /dev/sd#

/dev/sda:

 Model=ST3250820AS                             , FwRev=3.AAE   , SerialNo=            9QE150Y2
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=8192kB, MaxMultSect=16, MultSect=?1?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=488397168
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 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

/dev/sdb:

 Model=SAMSUNG HD321KJ                         , FwRev=CP100-10, SerialNo=S0MQJ1SP200375      
 Config={ Fixed }
 RawCHS=16383/16/63, TrkSize=34902, SectSize=554, ECCbytes=4
 BuffType=DualPortCache, BuffSize=16384kB, MaxMultSect=16, MultSect=?1?
 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 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-3,4,5,6,7
 * signifies the current active mode

/dev/sdc:

 Model=ST3500320AS                             , FwRev=SD15    , SerialNo=            9QM3Q44T
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs RotSpdTol>.5% }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=4
 BuffType=unknown, BuffSize=0kB, MaxMultSect=16, MultSect=?1?
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=976773168
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6 
 AdvancedPM=no WriteCache=enabled
 Drive conforms to: unknown:  ATA/ATAPI-4,5,6,7
 * signifies the current active mode

sudo hdparm -tT /dev/sd# on idle system:
/dev/sda:
 Timing cached reads:   2808 MB in  2.00 seconds = 1405.84 MB/sec
 Timing buffered disk reads:  236 MB in  3.03 seconds =  77.81 MB/sec
/dev/sdb:
 Timing cached reads:   2798 MB in  2.00 seconds = 1400.72 MB/sec
 Timing buffered disk reads:  244 MB in  3.02 seconds =  80.67 MB/sec
/dev/sdc:
 Timing cached reads:   2688 MB in  2.00 seconds = 1345.50 MB/sec
 Timing buffered disk reads:  328 MB in  3.02 seconds = 108.69 MB/sec

sudo hdparm -tT /dev/sd# coping 2GB file from sda to sdc:
/dev/sda:
 Timing cached reads:   1920 MB in  2.00 seconds = 960.25 MB/sec
 Timing buffered disk reads:   46 MB in  3.13 seconds =  14.71 MB/sec
/dev/sdb:
 Timing cached reads:   2728 MB in  2.00 seconds = 1365.05 MB/sec
 Timing buffered disk reads:  244 MB in  3.01 seconds =  81.17 MB/sec
 /dev/sdc:
 Timing cached reads:   2688 MB in  2.00 seconds = 1345.69 MB/sec
 Timing buffered disk reads:  274 MB in  3.02 seconds =  90.87 MB/sec

Similar results coping or moving from sda to sdb (no effect if coping between sdb and sdc). Same using cp/mv in terminal. 
BIOS settings have no effect (except disable sata controller :D). After clean install performance great (transfer speed 50MB), but after few days its go down to 4-10MB. Tried installing to other disk, same results. Manually add disk looks not effected by this (if make disk /home its slow down). /etc/fstab changes no effect to.

Other test (IOzone, Flexible IO Tester) give normal results or better than hdparm. 

Help!!!