Poweredge 800 multi-disk SATA slowdown?

[Brendan Conoboy]

Jeff Garzik wrote:
> Turn on AHCI mode for full speed.

Thanks Jeff, that certainly explains a few things.

As for turning on AHCI mode, I'm guessing that is what "RAID" mode is in 
the BIOS (As opposed to Legacy ATA).  There's a few problems with making 
this change, though:

1.  When I tried making the change and rebooting the system, the BIOS 
warned me that this change would cause data loss.  Perhaps this is 
because the BIOS will be writing some RAID metadata to my 
already-allocated drives.  This I can get by with a dump and reinstall 
of my system (currently in progress).

2.  According to the docs at:

http://support.dell.com/support/edocs/systems/pe800/en/UG/k3843c30.htm#wp1057684

The options: SATA Controller / (ATA default)

Allows the integrated SATA controller to be set to Off, ATA, or RAID. 
Off disables the SATA subsystem. ATA sets the SATA subsystem to Native 
IDE mode. RAID sets the SATA subsystem to RAID mode.

NOTE: RAID mode supports two drives (0 and 1). ATA mode supports all 
four drives.

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Does anybody on the list know if this is indeed the switch needed to 
enable AHCI?  If so, it looks like only two drives are going to work, 
which is a real drag.

Anyone?

-Brendan (blc at redhat.com)