Re: sata raid controller



On Friday 20 February 2009 04:05, someone identifying as *Amadeus W.M.*
wrote in /comp.os.linux.hardware:/

On Fri, 20 Feb 2009 02:24:45 +0000, Roger Blake wrote:

On 2009-02-20, Amadeus W.M. <amadeus84@xxxxxxxxxxx> wrote:
Could someone recommend a PCI-X sata raid controller that 1) works out
of the box with recent kernel releases (e.g. >= 2.6.27) 2) is 100%
hardware

3Ware RAID controllers are well-supported in Linux and have worked with
the mainstream kernel for quite a while now. Not sure if 3Ware makes a
PCI-X model. (Assuming you really do mean PCI-X and not PCI Express.)

How terrible would a software controller be?

Linux software RAID works well but I think can only boot from RAID 1
(mirrored disks). If you wanted to use, say, software RAID 5 you would
need to have a separate boot disk.

Thanks for the answer, will look into 3ware.

I do mean PCI-X because that's what the motherboard manual says.

Adaptec has SAS/SATA and pure SATA RAID controllers for both PCIe and PCI-X.
It's my favorite RAID and SCSI adapter brand. The SAS/SATA and SATA
controllers use the /aacraid/ driver, which is in every modern Linux kernel
and has already been included in the vanilla sources for many years.

You'll need this driver only for the device itself, though, because the RAID
functionality is entirely done in hardware and is "invisible" to the kernel
- i.e. with the exception of some individual disk monitoring capabilities
for the Linux kernel offered through the driver. The kernel sees all disks
in an array as being a single disk drive.

RAID 1 is what I want anyway, but I imagine software RAID would take up
cpu any time I access the disk, wouldn't it? How big of an issue is this?

Not so much of an issue as one might thing, or at least not in the Linux
kernel. I have no experience with other operating systems, though.

One more question, with a raid controller, do I need to create a ramdisk
with the appropriate driver so I can boot? Is that by any chance done
automatically for me upon install (say F10)?

Well, that depends. I'm not too well-versed on 3Ware, but if you're going
with Adaptec, then the /aacraid/ driver module would normally already be in
your /initrd/ if you use a distribution-built modular kernel, because this
very same driver is common to most of Adaptec's recent PCIe/PCI-X hardware
RAID controllers. It's just as ubiquitous as a Realtek 8139 NIC, and so
it's typically included in the /initrd/ per default.

I've installed a CentOS 5.1 a while ago on a machine with an U320 SCSI PCI-X
RAID controller by Adaptec which uses the same driver, and it was
recognized upon installation. Now CentOS is in essence the same thing as
RedHat and is thus not so bleeding edge, so if you go for something more
cutting edge like Fedora, OpenSuSE, Mandriva, Gentoo or whatever,
the /aacraid/ driver will certainly be included in the /initrd/ per
default.

(Note: If you decide to roll your own kernel, then I recommend statically
linking the driver into the kernel itself, as opposed to using a module.)

Adaptec cards come with driver modules, but it's always best to use the one
supplied in the Linux kernel you are using, because it'll probably be more
up to date. It's a GPL'ed driver and so its code is supplied by Adaptec to
the Linux vanilla source tree.

--
*Aragorn*
(registered GNU/Linux user #223157)
.