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Thread: Ubuntu To Try Switching From DMRAID To MDADM

  1. #1
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    Default Ubuntu To Try Switching From DMRAID To MDADM

    Phoronix: Ubuntu To Try Switching From DMRAID To MDADM

    Besides wanting to enable SSD TRIM support for Ubuntu Linux, developers are also looking at moving from DMRAID to MDADM for fake/software RAID configurations on the desktop operating system...

    http://www.phoronix.com/vr.php?view=MTUxOTk

  2. #2
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    Quote Originally Posted by phoronix View Post
    Phoronix: Ubuntu To Try Switching From DMRAID To MDADM

    Besides wanting to enable SSD TRIM support for Ubuntu Linux, developers are also looking at moving from DMRAID to MDADM for fake/software RAID configurations on the desktop operating system...

    http://www.phoronix.com/vr.php?view=MTUxOTk
    "on the desktop operating system"... (?) Does this mean ubuntu server will not be moving to mdadm? Is the raid configuration going to be somehow tied to the GUI? Inquiring minds want to know!

  3. #3
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    I've only ever used mdadm on Ubuntu. 12.04 LTS RAID 6 mdadm to be exact on my workstation with 5x 2TB disks. I need to re-read the posting because I've never heard of or used DMRAID. What am I missing?

  4. #4
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    Quote Originally Posted by Tgui View Post
    I've only ever used mdadm on Ubuntu. 12.04 LTS RAID 6 mdadm to be exact on my workstation with 5x 2TB disks. I need to re-read the posting because I've never heard of or used DMRAID. What am I missing?
    AFAIK, dmraid is more for hardware based or BIOS-created software RAID setups. mdadm is purely software RAID. Nowadays, you might as well just shoot for mdadm since it seems to be updated more often and RAID is hardly a stressor to CPUs.

    Its been a while since I've done anything RAID related but I think I used dmraid to set up my RAID configuration but I use mdadm to mount and access it, but I honestly don't remember. Unfortunately I have Windows access the array so don't think I was able to strictly use mdadm.

  5. #5
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    Quote Originally Posted by schmidtbag View Post
    AFAIK, dmraid is more for hardware based or BIOS-created software RAID setups. mdadm is purely software RAID. Nowadays, you might as well just shoot for mdadm since it seems to be updated more often and RAID is hardly a stressor to CPUs.

    Its been a while since I've done anything RAID related but I think I used dmraid to set up my RAID configuration but I use mdadm to mount and access it, but I honestly don't remember. Unfortunately I have Windows access the array so don't think I was able to strictly use mdadm.
    Thanks!

    I figured that software RAID would be best for me since I don't have to worry about a controller dieing on me.

  6. #6
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    Quote Originally Posted by Tgui View Post
    Thanks!

    I figured that software RAID would be best for me since I don't have to worry about a controller dieing on me.
    That's actually a great idea. In the times I've had to set up software raid because of cheap server equipment (read no hardware raid controller), I have had the unfortunate opportunity to try to work with FakeRAID (which is really what DMRAID is) and it never freaking works right. Namely because grub can't boot from specific types of RAID.

    So even then, I end up disabling the FakeRAID controller and going with mdadm.

    I was confused when I read the title and thought "Wtf, they don't already use mdadm?" I tend to stay away from Ubuntu in all it's forms, due to... well most people on here probably already know. I stick with pure Debian.

  7. #7
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    Quote Originally Posted by Tgui View Post
    I've only ever used mdadm on Ubuntu. 12.04 LTS RAID 6 mdadm to be exact on my workstation with 5x 2TB disks. I need to re-read the posting because I've never heard of or used DMRAID. What am I missing?
    I thought that dm supports ssd discard (trim) for intel soft raid sets including 0 and 10 whereas md supports raid trim for only jbod or possibly also 1. But maybe this is no longer the case?

  8. #8
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    With the broader move towards MDADM for Linux RAID administrator, Ubuntu developers are looking to follow this movement and transition to MDADM by default.
    Being Canonical, shouldn't they be reinventing the wheel a couple more times (and do a poor job of it)?

  9. #9
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    mdadm only supports intel raid. the problem is that the default name is Volume0, this name does not really work well. If you create intel raid then use a name without a number at the end and it will work fine to boot from (in the case you use raid 0, if you use 1 or 5 then it will only boot after it has been synced). dmraid has the main problem now that it does not support gpt at all, that means you can access gpt partitions not in the initrd, if you call partprobe (from parted) later then gpt partitions will appear as well but by default you only see mbr ones. i patched gparted (newer versions should not need that patch) to be able to format fat partitions on md devices for uefi boot, thats no problem at all. you can directly boot from uefi as well via mdadm but you always need an initrd. i tested that long ago, but ubuntu is always late

  10. #10

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    Quote Originally Posted by Kano View Post
    mdadm only supports intel raid. the problem is that the default name is Volume0, this name does not really work well. If you create intel raid then use a name without a number at the end and it will work fine to boot from (in the case you use raid 0, if you use 1 or 5 then it will only boot after it has been synced). dmraid has the main problem now that it does not support gpt at all, that means you can access gpt partitions not in the initrd, if you call partprobe (from parted) later then gpt partitions will appear as well but by default you only see mbr ones. i patched gparted (newer versions should not need that patch) to be able to format fat partitions on md devices for uefi boot, thats no problem at all. you can directly boot from uefi as well via mdadm but you always need an initrd. i tested that long ago, but ubuntu is always late
    Yeah, Fedora's been using mdraid for Intel firmware RAID and installer-created software RAID for at least four years.

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