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lollercoaster
Asked: 2011-06-19 17:37:18 +0800 CST

How to (hardware) RAID 10 on Ubuntu 10.04 LTS with 4 drives and motherboard with RAID contoller

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I have 4 500GB hard drives.

I set up a RAID 10 in BIOS, much like shown here: http://www.supermicro.com/manuals/other/RAID_SATA_ESB2.pdf

Then I followed these instructions: http://www.unrest.ca/Knowledge-Base/configuring-mdadm-raid10-for-ubuntu-910

Basically I cannot get it to work. I go through the instructions when I get to the "partition" section of the install, creating 4 RAID 1's (2 partitions on each drive, one for primary and one for swap space), then combining to make a RAID 10. Unfortunately it still shows 2 partitions, one 500 GB and another being 36GB for some reason. Any ideas?

I think best would be if anyone had found good instructions (step by step) for how to do this...I've been googling for hours and haven't found anything...

linux ubuntu raid hardware-raid raid10

4 Answers

  1. Your motherboard does not have an hardware RAID controller, but rather a SoftRAID one. That's basically a standard SATA controller + custom BIOS and drivers to work in raid mode. There's no cache, prefetch, parity (RAID5, RAID6), etc... it's best described as a software raid with BIOS support.

    Performance wise there is no (hardware) difference between the two solutions, which one performs better only depends on their respective software implementations (md and dmraid drivers, both in linux kernel). The low level disk access will be through linux SATA drivers in both cases (ie. the kernel will see and work with the individual disks under the hood).

    Whether to prefer using that or native linux software (mdadm) is another (long) story, but basically:

    • if you want to use your motherboard's soft raid you must not use mdadm but dmraid. Bonus point here is being able to boot from a RAID0 array or a degraded RAID1/RAID10 array. Could be tricky to get access to your data if the motherboard dies and you need to move to a different one.
    • if you want to use Linux software raid you must configure your motherboard controller as a standard SATA one and then use mdadm. Bonus point here is using standard and proven linux tools (md driver and mdadm utility) and being hardware-independent. You cannot boot from RAID0/10/5/6/otherfancystuff arrays, you can boot from RAID1 arrays if you do your homework right.

    If you follow the motherboard's softraid way, you have to find how to create a RAID10 setup before actually installing/booting linux, as described in the manual. But keep in mind you have no true hardware raid.

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  2. Firstly you don't want to use mdadm because that is for software RAID. Secondly Why are you creating 4 RAID 1's? What you want to do is create 2 RAID 1's and then use them to create a RAID O. Example Use Drive 1+2 to create a RAID 1 (lets call it R1). Similarly use drive 3+4 to create RAID 1 (R2). Then use R1+R2 to create a RAID 0

    Once you setup up RAID in your BIOS you want to install ubuntu normally because a hardware RAID is transparent to the OS.

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  3. Sameer is correct that you don't need to worry about mdadm at all because that is for software RAID and as your motherboard has hardware RAID that is preferred over software even on the worst day. Sameer is slightly incorrect in the inner workings of how a RAID10 array is configured but that is not germane to the question at hand. RAID10 involves the stripping (concatenating) of 2 pairs of drives (RAID0). These 2 striped arrays are then mirrored (RAID1).

    The PDF you linked actually gives you the instructions to configured RAID10 on page 6. You would need to perform this before you attempt to install Ubuntu. Once the RAID10 volume is created when you install Ubuntu it should be seen as a 1TB SCSI device (most likely /dev/sda) to the OS.

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  4. First you do not have hardware raid. I've checked the stats on Intel's website. What you have is software raid (softraid) AKA "fakeraid".

    http://ark.intel.com/products/codename/26738

    In this, the operating system handles the raid in software, with assistance from the BIOS. Windows includes a driver for it that makes it look like a hardware raid, but it is not. They way to test it, is to see how many hard drives Linux sees it as: If you see the individual drives (as you do) that's a softraid. A hardware RAID would (a) cost about 300 dollars for the controller, and (b) have an all-in-1 drive controller that made all the drives appear as 1 to Linux.

    Check the ubuntu documenation for softraid, they explain the difference between hardware raid and softraid and how to set it up. I used mdadm for mine. Raid on linux is a pain.

    https://help.ubuntu.com/community/FakeRaidHowto

    https://help.ubuntu.com/community/Installation/SoftwareRAID

    EDIT: I have to say Luke04's answer is good.

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