Growing RAID-10 (near-2) array - which kernel needed?

Growing RAID-10 (near-2) array - which kernel needed?

[cvb]

Apologies for raising this topic again, but I can't seem to find 
anything googling, and man mdadm doesn't also give me a clue. Which 
kernel version is needed to grow a near-2 RAID 10 array?

I'm currently running kernel 3.13.0 with mdadm 3.2.5. But I could also 
use a live CD with a newer kernel, if needed.

I have replaced the 4 disks here with larger ones (2TB drives -> 4 TB 
drives), and this is what the array currently looks like:

# mdadm --detail /dev/md0
/dev/md0:
         Version : 1.2
   Creation Time : Sat Aug 20 08:15:07 2011
      Raid Level : raid10
      Array Size : 3906764800 (3725.78 GiB 4000.53 GB)
   Used Dev Size : 1953382400 (1862.89 GiB 2000.26 GB)
    Raid Devices : 4
   Total Devices : 4
     Persistence : Superblock is persistent

     Update Time : Thu Dec 11 08:31:15 2014
           State : clean
  Active Devices : 4
Working Devices : 4
  Failed Devices : 0
   Spare Devices : 0

          Layout : near=2
      Chunk Size : 512K

            Name : alpha:0  (local to host alpha)
            UUID : 8199e640:58fc3a04:99b52fe6:80a1574d
          Events : 918971

     Number   Major   Minor   RaidDevice State
        6       8        1        0      active sync   /dev/sda1
        5       8       33        1      active sync   /dev/sdc1
        7       8       17        2      active sync   /dev/sdb1
        4       8       49        3      active sync   /dev/sdd1

Re: Growing RAID-10 (near-2) array - which kernel needed?

[Robin Hill]

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On Thu Dec 11, 2014 at 07:31:31PM +0100, cvb@kruemel.org wrote:

> Apologies for raising this topic again, but I can't seem to find 
> anything googling, and man mdadm doesn't also give me a clue. Which 
> kernel version is needed to grow a near-2 RAID 10 array?
> 
Full reshape support (changing number of devices, layout or chunk size)
was introduced in 3.5 (http://kernelnewbies.org/Linux_3.5).

> I'm currently running kernel 3.13.0 with mdadm 3.2.5. But I could also 
> use a live CD with a newer kernel, if needed.
> 
It also requires mdadm 3.3 or above.

> I have replaced the 4 disks here with larger ones (2TB drives -> 4 TB 
> drives), and this is what the array currently looks like:
> 
> # mdadm --detail /dev/md0
> /dev/md0:
>          Version : 1.2
>    Creation Time : Sat Aug 20 08:15:07 2011
>       Raid Level : raid10
>       Array Size : 3906764800 (3725.78 GiB 4000.53 GB)
>    Used Dev Size : 1953382400 (1862.89 GiB 2000.26 GB)
>     Raid Devices : 4
>    Total Devices : 4
>      Persistence : Superblock is persistent
> 
>      Update Time : Thu Dec 11 08:31:15 2014
>            State : clean
>   Active Devices : 4
> Working Devices : 4
>   Failed Devices : 0
>    Spare Devices : 0
> 
>           Layout : near=2
>       Chunk Size : 512K
> 
>             Name : alpha:0  (local to host alpha)
>             UUID : 8199e640:58fc3a04:99b52fe6:80a1574d
>           Events : 918971
> 
>      Number   Major   Minor   RaidDevice State
>         6       8        1        0      active sync   /dev/sda1
>         5       8       33        1      active sync   /dev/sdc1
>         7       8       17        2      active sync   /dev/sdb1
>         4       8       49        3      active sync   /dev/sdd1
> 
I can't find anything explicitly covering growing a RAID 10 by just
increasing the device sizes. I would have thought that would be an
easier task than doing so by adding disks, so should be supported in an
earlier version. mdadm 3.2.1 mentions supporting converting between
RAID-10 and RAID-1, which can definitely be grown.

Have you tried doing a grow with the versions you have?

Cheers,
    Robin

-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: Growing RAID-10 (near-2) array - which kernel needed?

[NeilBrown]

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On Thu, 11 Dec 2014 19:21:39 +0000 Robin Hill <robin@robinhill.me.uk> wrote:

> On Thu Dec 11, 2014 at 07:31:31PM +0100, cvb@kruemel.org wrote:
> 
> > Apologies for raising this topic again, but I can't seem to find 
> > anything googling, and man mdadm doesn't also give me a clue. Which 
> > kernel version is needed to grow a near-2 RAID 10 array?
> > 
> Full reshape support (changing number of devices, layout or chunk size)
> was introduced in 3.5 (http://kernelnewbies.org/Linux_3.5).
> 
> > I'm currently running kernel 3.13.0 with mdadm 3.2.5. But I could also 
> > use a live CD with a newer kernel, if needed.
> > 
> It also requires mdadm 3.3 or above.
> 
> > I have replaced the 4 disks here with larger ones (2TB drives -> 4 TB 
> > drives), and this is what the array currently looks like:
> > 
> > # mdadm --detail /dev/md0
> > /dev/md0:
> >          Version : 1.2
> >    Creation Time : Sat Aug 20 08:15:07 2011
> >       Raid Level : raid10
> >       Array Size : 3906764800 (3725.78 GiB 4000.53 GB)
> >    Used Dev Size : 1953382400 (1862.89 GiB 2000.26 GB)
> >     Raid Devices : 4
> >    Total Devices : 4
> >      Persistence : Superblock is persistent
> > 
> >      Update Time : Thu Dec 11 08:31:15 2014
> >            State : clean
> >   Active Devices : 4
> > Working Devices : 4
> >   Failed Devices : 0
> >    Spare Devices : 0
> > 
> >           Layout : near=2
> >       Chunk Size : 512K
> > 
> >             Name : alpha:0  (local to host alpha)
> >             UUID : 8199e640:58fc3a04:99b52fe6:80a1574d
> >           Events : 918971
> > 
> >      Number   Major   Minor   RaidDevice State
> >         6       8        1        0      active sync   /dev/sda1
> >         5       8       33        1      active sync   /dev/sdc1
> >         7       8       17        2      active sync   /dev/sdb1
> >         4       8       49        3      active sync   /dev/sdd1
> > 
> I can't find anything explicitly covering growing a RAID 10 by just
> increasing the device sizes. 

commit 006a09a0ae0a494473a8cd82c8d1d653e37e6663
Author: NeilBrown <neilb@suse.de>
Date:   Mon Mar 19 12:46:40 2012 +1100

    md/raid10 - support resizing some RAID10 arrays.


$ git describe --contains 006a09a0ae0a494473a8cd82c8d1d653e37e6663
v3.4-rc1~147^2~8

So Linux-3.4 is needed.
I don't think you need a particularly new mdadm.

NeilBrown

>                              I would have thought that would be an
> easier task than doing so by adding disks, so should be supported in an
> earlier version. mdadm 3.2.1 mentions supporting converting between
> RAID-10 and RAID-1, which can definitely be grown.
> 
> Have you tried doing a grow with the versions you have?
> 
> Cheers,
>     Robin
> 


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Re: Growing RAID-10 (near-2) array - which kernel needed?

[cvb]

> Have you tried doing a grow with the versions you have?

Not yet, I thought it'd be wise to ask first, as this appears to be 
nowhere documented. And I like restricting the cases where I need to 
revert to my backup to the absolute minimum. :-)

Thanks, Chris

Re: Growing RAID-10 (near-2) array - which kernel needed?

[cvb]

> So Linux-3.4 is needed.
> I don't think you need a particularly new mdadm.

Ok, thanks. Will try it with what I have, and report back.

Chris