Re: Creating an md with 3TB drives.

On 28/09/2011 17:09, Marcin M. Jessa wrote:

On 9/28/11 10:43 AM, David Brown wrote:

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On 28/09/2011 10:31, Marcin M. Jessa wrote:

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On 9/28/11 10:23 AM, NeilBrown wrote:
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Then I used fdisk to change the partition type to Linux raid auto

You can do that if you like but it will have no effect. The "raid auto"
partition type only means anything on MBR partitions. You don't need
to, so
don't bother.

Thanks Neil.
Not using fdisk worked like a charm.

Using fdisk probably resulted in the disks going over to MBR rather than
GPT, and thus you have a 2TB limit.

By the way, you should probably try the parted again and fix the
alignment issue (rather than just "ignoring" it) - it will make a /big/
difference.

In terms of speed?
This RAID array is temporarily just so I can back up/restore my broken
5x2TB RAID6 but it would be interesting to know what to do.
I was running
# parted -a optimal /dev/sdd
which was suppose to fix that warning but it didn't.

Yes, I was thinking in terms of speed.  I haven't gone beyond 2 TB disks with MBR myself, so I can't comment on whether your partitions really are misaligned, or if it is just an incorrect warning.  But if these disks are like most 2 TB disks with 4K sectors but which lie and claim to have 512 byte sectors (for compatibility with ancient and inferior OS'es), then partition misalignment will be major performance hit.  It's worth double-checking that you've got it right here, before you go to far with the array.