[K12OSN] RAID5 so slow?

[Mella]

Hi!

I test 2 similar computers today. Almost similar except SCSI controllers 
and kernels.
I found RAID5 2x slower than disks separately in other computer. Is it 
normal or I have some misconfigutations in Intel controller or default 
FC3 kernel?

Computer 1- Intel HG2 MB, DualXeon 2,8GHz, Intel RAID U320 add-on 
controller with 3 disks RAID5 array.

array (sda) 3x73GB Atlas 10K3 Kernel 2.6.11-1.14_FC3smp #1 SMP

[root at ts ~]# hdparm -t /dev/sda
/dev/sda: Timing buffered disk reads:   82 MB in  3.02 seconds =  27.18 
MB/sec

Computer 2 - Intel VB2 DualXeon 2,4GHz, Adaptec U160.
Disk (sda) 36GB Atlas 10K4 Kernel 2.4.30-1.smp.dma #1 SMP (self compiled)

[root at mail root]# hdparm -t /dev/sda
/dev/sda: Timing buffered disk reads:  64 MB in  0.95 seconds = 67.37 
MB/sec
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Why faster disk and controller give slower performance data with RAID?