mdadm on same drive ?

Discussion in 'Computers, Hardware, and Operating Systems' started by AA7EJ, Aug 24, 2016.

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  1. AA7EJ

    AA7EJ Ham Member QRZ Page

    OK, it's me again with silly stuff.
    Reason I am here - I am getting nowhere with "official" forums. More than one!

    Being paranoid I want to implement software RAID.
    Being double paranoid I want to test it.

    Basic question - can I build RAID on SAME drive - just to test?

    I can follow mdadm implementation and run mdadm on DIFFERENT drives but cannot save anything in the array.
    Mainly because after I start / run md0 GParted will find md127 instead!

    Secondary question - can I really add RAID partitions into working drive?
    I am not using boot drive to do this test.

    Third question - why does GParted find "unimplemented" device "md0" or "md127"?

    73 Shirley
  2. KK4NSF

    KK4NSF Ham Member QRZ Page

    that's an interesting question.... and to be honest, I don't know, since I've never tried. BUT it seems like you should be able to create two identical partitions on a single drive, and then set them up as a RAID array. I'd not be comfortable trying to do this with the Boot Drive, or with an already working drive that contained any data that had not been completely backed up.

    However, setting up two RAID partitions on a single drive sort of defeats part of the purpose of having a RAID array, doesn't it?
  3. AA7EJ

    AA7EJ Ham Member QRZ Page

    I have tried but I think I forgot to set the config so it did not work.
    I am still not sure why GParted reports mdx device and it can be partitioned too.
    I think it may be what Widows build as part of "dynamic disk".
    I guess I need to decipher the doc , again.
    And yes, I just want to test it and I did stay away from boot drive!
  4. KA8NCR

    KA8NCR Ham Member QRZ Page

    Considering RAID means Redundant Array Inexpensive Drives, agreed. I mean, the concept of trying to create RAID elements on the same drive is so counter to the purpose, I would be surprised the developers of the tools allowed it in the first place. If not on principle, just because of the chaos and name calling the resulting discussion would have brought on the developer mailing list.

    To the OP, if you want to get your feet wet with mdadm and Linux RAID, use a pair of cheapie USB drives. In fact, I highly recommend to anyone with your level of curiosity in the Linux operating system to insert a non-partitioned unformatted USB drive and start trying to write and read that data from the block device.
    Last edited: Aug 28, 2016
    KK4NSF and KF5RRF like this.
  5. KA8NCR

    KA8NCR Ham Member QRZ Page

    Because the kernel says it is there. Unless you destroy a metadevice, it remains there available to bind it to real devices, or not. But until you specifically tell it to go away, it stays.
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    " use a pair of cheapie USB drivesuse a pair of cheapie USB drives "
    Came to same conclusion.

    Still looking for explanation why GParted allows me to partition mdx.
    Found some mdxpx stuff. The suffix -p is specifically used for mdx partitions.

    PS Personally I have hard time, as always, understanding if I specifically said "for testing purpose on single driver " people get after me.
    That seems to be trendy on QRZ - no matter how specific the post, there is always somebody getting of the tangent.
    And if I suggest not to get off the subject people get offended AKA freedom of speech etc.
    It's a no win situation.
    Off soap box HI HI HI

    73 Shirley
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    Yes. And it is silly too.
  8. KA8NCR

    KA8NCR Ham Member QRZ Page

    Talking off the cuff here, or from more posterior parts...perhaps Gparted is happy working up a job list to partition these metadevices, but won't actually do anything when you stab the "doit" button?

    I don't think anyone here is taking exception to you wanting to make a metadevice out of two partitions on the same disk, I think the questioning is more along the lines of would the developers of said tools permit you to do it.
  9. KX4OM

    KX4OM Ham Member QRZ Page

    Are you near a Micro Center store? I just picked up an 80 GB SATA hard drive to do some testing as a USB 2.0 drive for my Raspberry Pi B+. It cost $2.95 plus tax. I'm replacing an old non-working PATA-IDE drive a few years back that I had mounted in a case that used to be a non-functioning 5.25 inch CD-ROM slide-in unit. It now has rubber feet on it. Separate power supply, of course for those 3.5 inch drives. I'm awaiting the slow boat from China with my $1.56 SATA interface to replace the PATA one. I do a lot of that type of hacking.

    Ted, KX4OM
  10. AA7EJ

    AA7EJ Ham Member QRZ Page

    And that was partially reason for this OP. I was and still not sure if it was my wrong mdadm configuration error it really did not function as RAID or because the mdadm did not care if the array is in same physical drive.

    Ted, I am checking on Micro Center after this post. Thanks for the suggestion.

    I just got a lecture from Arduino IDE hiding copy of source code after first run of the IDE.
    The more I am getting into the "compile your own" , more I realize how convoluted Arduino IDE is.
    Something about chewing gum and bailing wire comes to mind.
    But it works for simple projects and that was the original idea behind Arduino anyway, so as far as knows - success !

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