after installing ubuntu-server, HDD's are not detected in AHCI mode

[scar]

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i am really leaning towards a bug with ubuntu.

after changing the BIOS back to IDE mode and thus detecting the disks, i
booted up a livecd and proceeded to simply delete the partitions on the
disks with gparted.  then, rebooted and changed the BIOS back to AHCI.
the disks are magically detected again.

so, i go and install ubuntu-server again on a third, identical server.
upon rebooting, the disks are no longer detected.  the BIOS just gets
stuck at 'auto-detecting SATA PORT0'

i noticed something interesting in the installation, during the
partitioning.  both disks initially showed up as 'free space' but, as
soon as i carved out the partitions like i did last time, they magically
showed up as raid/lvm paritions.  so, something was still on the disks.
 maybe i need to use dd to write zeroes to the entire surface of both disks?

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