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-   -   Sata Raid 1 and Single Sata drive drive order issue (http://www.linuxquestions.org/questions/linux-hardware-18/sata-raid-1-and-single-sata-drive-drive-order-issue-538400/)

Kvetch 03-17-2007 10:08 PM

Sata Raid 1 and Single Sata drive drive order issue
 
Hello, I am having some issues getting my system (Epox 9npa+ultra with nvidia raid) to see my drives in the right order. I have a single SATA drive and now I recently purchased two new sata drives. I set them up in a raid 1 mirror. The single drive is connected to the first sata connection and then the other two on sata connections 3 & 4. For some reason when I boot into Linux (Gentoo) it sees the RAID mirror as the first scsi device and not the single sata as it use to. So fdisk -l shows the raid is now sda and sdb and the single is sdc. I am not sure why it is seeing the raid as separate drives either. I thought it would only see one drive.
Anybody have any clues as to how I can get the raid to be lower on the scsi chain than the single drive and why does it show them as separate drives?

Thanks,
Nick

Quakeboy02 03-17-2007 10:11 PM

Some of your questions are answered here:

http://linux-ata.org/faq-sata-raid.html

Kvetch 03-18-2007 10:54 AM

Thanks Quakeboy, I saw another post talking about dmraid but I was really hoping I wouldn't have to use it.

Kvetch 03-18-2007 04:55 PM

Since this is not going to be my primary drive and I do not dual boot would it just be better to use the kernel's software raid?

Quakeboy02 03-18-2007 05:11 PM

"Since this is not going to be my primary drive and I do not dual boot would it just be better to use the kernel's software raid?"

Ah, I see the confusion. DMRAID uses the kernel's software raid. I've given this before, but here is a simplified version of how Linux used FakeRaid devices.

First off, the case where you're booting from a FakeRaid. The BIOS uses the code in the FakeRaid to read the data off the disks in proper order so that you can boot. During Linux boot, at some point the kernel is loaded to memory and needs to take control of the disk drives - this is true whether it's an IDE disk, an ATAPI DVD/CD, or a FakeRaid. In the case of FakeRaid, the DMRAID software reads what is called metadata from the first device in the array. It uses this to figure out whether the data is striped or mirrored, and configures kernel access, accordingly, and Linux goes merrily along its way.

In the case of not booting from the array, then the kernel once again uses DMRAID to read the metadata and configure access to the array. But, either way, the configuration entails using the kernel's "software RAID" modules to access the array. The difference is that you don't have to get personally involved in actually configuring the array with "mdadm" when you use "dmraid" with a FakeRaid device.

Does that help?

Kvetch 03-19-2007 07:50 PM

Yes it does, thanks. I have used the kernel's software raid before and have no issues using mdadm instead of the bios raid so I will probably just use the kernel raid by itself and not use the dmraid.

Thanks,
Nick


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