This is a general warning: Do not use megaraid SATA RAID controllers (LSI Logic / Symbios Logic PowerEdge Expandable RAID Controller 4 (rev 01), also rebranded and sold by major manufacturers).

We had a machine with both Linux 2.4 and 2.6 running (various versions), Seagate and WDC disks, tried to tune software and BIOS parameters. Nothing helped. This is what we took out of order:

megaraid cmm: 2.20.2.5 (Release Date: Fri Jan 21 00:01:03 EST 2005)
megaraid: 2.20.4.5 (Release Date: Thu Feb 03 12:27:22 EST 2005)
megaraid: fw version:[713G] bios version:[G117]
scsi0 : LSI Logic MegaRAID driver

This controller does not deliver more than 6MB/s when reading from a mirrored RAID. Sustained write performance is something like 4MB/s, but that's not the worst part: You can write very quickly to it until the on-board cache is full (64MB). While this cache is being flushed the host system comes to a complete halt since …