OK.  We've found a potential issue.  Are the disks being identified as
UDMA-33 or UDMA-66/100/133?  The performance numbers agree too closely for
this to be a coincidence.  Check the boot logs.

I looked into /var/log/dmesg and found this:

blk: queue c0393144, I/O limit 4095Mb (mask 0xffffffff)
hda: 39062500 sectors (20000 MB) w/2048KiB Cache, CHS=2431/255/63, UDMA(33)
blk: queue c03934a8, I/O limit 4095Mb (mask 0xffffffff)
hdc: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=232581/16/63,
UDMA(33)
blk: queue c039380c, I/O limit 4095Mb (mask 0xffffffff)
hde: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=232581/16/63,
UDMA(33)
blk: queue c0393b70, I/O limit 4095Mb (mask 0xffffffff)
hdg: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=232581/16/63,
UDMA(33)
blk: queue c0393ed4, I/O limit 4095Mb (mask 0xffffffff)
hdi: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=232581/16/63,
UDMA(33)
blk: queue c0394238, I/O limit 4095Mb (mask 0xffffffff)
hdk: 234441648 sectors (120034 MB) w/2048KiB Cache, CHS=232581/16/63,
UDMA(33)

This is what you meant?

but after the boot I set hdparm manually for each drive with the following
settings:

hdparm -a8 -A1 -c1 -d1 -m16 -u1 /dev/hdc.