I'm migrating a PC working as file server from Gentoo to Ubuntu. Gentoo doesn't recognize the RAID by BIOS because apparently Gentoo connects with each and every individual hard drive directly.
Anyone knows if Ubuntu works the same way, when RAID is provided by integrated controller in the motherboard and by the BIOS ?
I'm using an Gigabyte FX-990 UD5 board with 2TB caviar black HDs.
That has nothing to do with the distro. It sounds like your board is a little funky when it comes to general Linux support.
http://www.amazon.com/review/R1LPS5LC21G3ZA/ref=cm_cr_pr_viewpnt#R1LPS5LC21G3ZA
This board is not directly compatible with Linux, specifically the built-in Ethernet. In order for it to work you must enable IOMMU in BIOS, but disable IOMMU on the linux kernel command line with “iommu=soft”. Without this all will appear working, but you will have absolutely no connectivity. This bug / compatibility issue affects all revisions past 1.1 that have the new UEFI BIOS.
So IOMMUs are usually a nice to have for virtualized environments, it basically lets you assign pci devices to virtual hosts. Why you would need to explicitly enable it to gain access to your RAID controller is weird. iommu=soft is really bad news for performance.
https://www.kernel.org/doc/Documentation/x86/x86_64/boot-options.txt
General iommu options:
off Don't initialize and use any kind of IOMMU.
noforce Don't force hardware IOMMU usage when it is not needed.
(default).
force Force the use of the hardware IOMMU even when it is
not actually needed (e.g. because < 3 GB memory).
soft Use software bounce buffering (SWIOTLB) (default for
Intel machines). This can be used to prevent the usage
of an available hardware IOMMU.
What that means is the kernel has to copy whatever it needs to read/write to an intermediate location before it can complete the DMA. So at least a 2x latency hit.
You might be better off without it honestly. Consider using a different board for more intense server applications.
