[CentOS] mdadm size issues

Stephen Harris lists at spuddy.org
Thu Sep 24 10:47:47 UTC 2009


On Thu, Sep 24, 2009 at 03:48:35PM +1000, Nathan Norton wrote:

> I am trying to create a 10 drive raid6 array. OS is Centos 5.3 (64 Bit)
> 
> All 10 drives are 2T in size.

> Disk /dev/sda: 2000.3 GB, 2000398934016 bytes

> mdadm: size set to 1953511936K
> Continue creating array?
> 
> As you  can see mdadm sets the size to 1.9T. Looking around there

But later...

> # mdadm --detail /dev/md3
> /dev/md3:
>         Version : 0.90
>   Creation Time : Thu Sep 24 23:48:32 2009
>      Raid Level : raid6
>      Array Size : 15628095488 (14904.11 GiB 16003.17 GB)

That's a little bit bigger than 2T :-)  Indeed, it looks around right.

Assuming all disks are the same size, then to a first approximation
you would have this much space in your raid6:
  8*2000398934016/1024 = 15628116672 KiB
          mdadm reports  15628095488

I think the difference falls within expected limits.

> Anyone got any ideas?

The "create" line may have reported a small value (it reported the size
of each disk), but the final array looks nice and big.

-- 

rgds
Stephen



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