RAID10 disk layout configuration

  • After trying out some of the other NAS O.S., I installed OMV and created a RAID 10 array and then formated with ext4 filesystem. I was surprized on how easy it was creating the RAID 1+0 array compared to others. This simplicity also raises some questions such as:
    How do I know / How do I specify which of my disks are mirrored together?
    (I have 2 WD and 2 Seagate drives - and I would like to mirror each WD with a Seagate, then have them striped together)
    Here is a link that talks about this:http://www.finnie.org/2012/11/…x-md-raid-10-disk-layout/


    Also, how would I specify a certain Chunk size?


    I'm liking Open Media Vault so far, but I'm shocked at how little documentation / guides there is, when compared to others.


    (PS: I don't have much experience in Linux, but I'm not affraid of the CLI)

  • Thanks, but yes, I've seen it. Both of the links under LVM/RAID focus on RAID5 configuration.
    For example, I was expecting that the WIKI RAID page (http://wiki.openmediavault.org…php?title=RAID_Management) would say at least something like this:
    (I'm bluffing here, so don't take the phrases below as info about how OMV works)
    "The RAID levels on the Graphical Web interface of the OMV uses the Linux command mdadm"
    "These options are only for whole disk RAID arrays, not partitions"
    "The RAID10 option will mirror the disks in the order that they are selected. 1st and 2nd selection will be a mirror and 3rd and 4th will be a mirror. This option will create a chunk size of 4096 bytes. For a different chunck size, the RAID 10 configuration will have to be done through the Command Line Interface. See <link> on getting to and using the CLI. See <link> for different mdadm options."

  • Not many people are using RAID 0+1 or RAID 1+0. That is why there is not much on it in forum. There have been discussions on chunk size. If you search forum for "chunk size" you will put up quite a few posts. I put link to the How Tos because many when they first come to forum have not noticed it.

  • I was hoping there would be more options during the creation of RAID10 array in the new version 1.0, but it looks like its the same simple design. I do like simplicity, but I think maybe there needs to be an option to enable advanced configurations. My question from the original post still remains: "How do I know / How do I specify which of my disks are mirrored together?"

    • Offizieller Beitrag

    If you are creating a raid 10 array, why would it matter which disks are mirror together? Most people use four identical disks. Like tekkb said, the 1+0 and 0+1 argument doesn't come up much.


    What "advanced configuration" do you want? If you really want an advanced configuration, create the array in systemrescuecd. OMV will see it.

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  • I'm not talking about 1+0 vs 0+1 debate.
    I have 2 WD and 2 Seagate drives - and I would like to mirror each WD with a Seagate, then have them striped together (aka RAID10, RAID1+0).
    Reason being: If WD or Seagate drives both came out of a bad batch of drives, and both drives fail simultaniously, I would not loose any data.


    Other advanced options would be: chunk-size, Stride, Stripe-Width

    • Offizieller Beitrag

    If you are that picky about setting up a raid array, you should have a backup and not lose any data :) Like I said, set up the array using systemrescuecd if you want to do that.


    I used to spend time messing with the options you mentioned and it never really produce noticeably different results (at least over gigabit networking) than the default OMV settings.

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  • lol,
    I'm trying to provide constructive criticism on ways to make the software even better / more flexible. I'm all for simplicity and I really like that someone can setup a raid10 array without worrying about minor details. But I still think that an option to show/hide advanced config. should be built into OMV.
    BTW, I think that choosing wich specific physical disk is mirrored to what other disk - is an essential (not advanced) feature.
    So the question still stands (i'll rephrase it): When creating a RAID10 array, does the order of selecting disks play any role?

  • kzrussian: Please create a feature request on the bugtracker under http://bugtracker.openmediavault.org


    Greetings
    David

    "Well... lately this forum has become support for everything except omv" [...] "And is like someone is banning Google from their browsers"


    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.

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  • I just submitted for these features. Thanks davidh2k, I never knew that option existed.


    Is there anyone that can answer this question:
    When creating a RAID10 array, does the order of selecting disks play any role?


    Thank you everyone for taking your time to answer my questions. I really appreciate it.

  • Well, if you don't come in here with a bulldozer opinion we are happy to discuss most things ;)


    Just to clarify, I was not saying that your opinion was bulldozer like, other people come in here with an attidude. Yours just reminded me a bit of them, allthough your concern is 100% valid.


    Greetings
    David

    "Well... lately this forum has become support for everything except omv" [...] "And is like someone is banning Google from their browsers"


    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.

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    Einmal editiert, zuletzt von davidh2k ()

    • Offizieller Beitrag

    I understand that you are providing constructive criticism. You are just the first in my years of being a mod saying this feature is essential. I even use raid 10 on my production server.


    I don't think anyone has ever checked. I doubt it. When you select the disks, the interface probably parses through the list in order that it is displayed not the order it was checked.

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  • "interface probably parses through the list in order that it is displayed not the order it was checked"
    That's what I'm thinking too, but hoping that its not the case. Is there a way anyone can confirm this?

  • Grab the 1.0 VM from sourceforge and play around.


    I also edited my post above.


    Greetings
    David

    "Well... lately this forum has become support for everything except omv" [...] "And is like someone is banning Google from their browsers"


    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.

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    • Offizieller Beitrag

    I don't see anything in the code that passes the order they were clicked. You could swap sata cables as well. Otherwise, file a request here.

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  • I played around with the online-demo a little bit and I notised that it does make a difference in the order in which the RAID10 drives are selected when creating the arrary.
    Here is an example of the array status in 2 different orders of selection.

    Code
    Number   Major   Minor   RaidDevice State
           0       8       16        0      active sync   /dev/sdb
           1       8       32        1      active sync   /dev/sdc
           2       8       48        2      active sync   /dev/sdd
           3       8       64        3      active sync   /dev/sde


    vs


    Code
    Number   Major   Minor   RaidDevice State
           0       8       16        0      active sync   /dev/sdb
           1       8       48        1      active sync   /dev/sdd
           2       8       32        2      active sync   /dev/sdc
           3       8       64        3      active sync   /dev/sde


    It appears that the GUI interface does pass the devices to the mdadm function in the same order as they are being selected.
    The mdadm function actually cares about the order of devices you give it.
    After doing a bit more reading about mdadm raid10 option, I have some more questions on how OMV uses it. ?(
    ryecoaaron (or anyone else who is able to), would you please be able to look at the code and tell me the 'command' that OMV uses when it creates a raid10 array?
    I would expect something like:

    Code
    mdadm --create -l 10 -n4 -pn2 [new device name] [device1] [device2] [device3] [device4]


    I'm asking because when configuring a RAID10 array, it is necessary to specify the number of replicas of each data block that are required (this will normally be 2) and whether the replicas should be 'near', 'offset' or 'far', so i'm curious to know how OMV implements this. :)


    Sorry for being such a pain-in-the-a$$, i guess i'm just a controll freek :S


    Thanks aggain for your time! :)

    • Offizieller Beitrag

    The code specifies device name, level, and number of devices. All other flags use their default settings.


    Not sure what the -pn2 flag is. I don't know why most users would need to change the replicas (I don't). Replicas seem to get away from raid's goal of redundancy and more toward backup. I honestly think you would be happier with greyhole.

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  • Linux offers the creation of standard and non-standard RAID.


    I too was interested in being to specify how I could use RAID10 in OVM and was disappointed that it forced me to use four drives. I have configured and used RAID10 with two drive sets, even when more were available. I have never had any issues with it and performances have been very good. In addition I love the fact that I don't have to worry if the drive case fails because the RAID configuration is elsewhere and as long as that is backed up, I have the ability to reconstruct the array and extract my data if need be or jump back into operation.


    One thing that we have to keep in mind is that no matter what other OS' do, what matters is what Linux can and is able to do. The default response when I tell some people that I build RAID10 from two or odd numbers of drives is "... it's impossible because you need four drives for RAID10 ... " That's what they've learned and by that I mean that it's what they have been told without understanding the premise of what was inculcated and so that what it is. When, in addition to the accepted a conclusion, one attempts to further their understanding into why what they have accepted is such, they find themselves in a better position to accept change because they can track the basis or bases of the change or changes. Ideologically Linux allows things which a few modern OS' do not or even allows for their adherent to conceptualize.


    I remember when I was trying to explain to someone why I was creating a LXC container inside of a VMWare virtual machine. Their argument was based on one construct of virtualization as if that was the only construct and never once stopped to question their premise and why it might be totally wrong. Linux is not only an alternative to other OS but it also offers alternative ways of accomplishing things and that requires that, though one knows what they know, they must realize that in the extent of what could be known they don't really know much. So it's the opportunities for learning and evolving that are important not how "right" we want to be or feel that we are.


    There is a nice segment devoted to non-standard Linux RAID formats
    https://en.wikipedia.org/wiki/Non-standard_RAID_levels


    Some other pages:
    http://www.ilsistemista.net/in…t-benchmark-analysis.html
    https://www.suse.com/documenta…data/raidmdadmr10cpx.html
    http://blog.a2o.si/2014/09/07/…aid-10-instead-of-raid-1/
    I have read that Linux' RAID10 is akin to RAID1E
    http://www.freeraidrecovery.com/library/raid-1e.aspx


    I do hope to see interfaces which aren't interested in conforming to accepted and well known but often limited views from other OS', as opposed to ones which allow access to the potential power of the OS. The bridge, I think, lies in flexible documentation.

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