On Thu, Feb 5, 2015 at 7:14 AM, NeilBrown <neilb@xxxxxxx> wrote:
> A v1.2 array normally has data from the data_offset all the way to the end of
> the device (maybe rounded down to chunk size).
Right. So in my case there were 5120 sectors unused at the start.
Unfortunately, I do not know whether the array initially had a 'size'
that included the trailing 3072 sectors or not.
What I do know: before reshape I had a chunk size of 512K and 4 disks
in raid5. When I created the array, tools at the time did not support
--data-offset, but I probably specified all the options I could find
saying I wanted 4M alignment. I reshaped the array from 1 disk to 2 to
3 to 4 as I added disks.
Unfortunately, I do not have a record of what 'mdadm -E' said before I
started the reshape.
Before I fixed the superblock:
Avail Dev Size : 5842897920 (2786.11 GiB 2991.56 GB)
Array Size : 8764342272 (8358.33 GiB 8974.69 GB)
Used Dev Size : 5842894848 (2786.11 GiB 2991.56 GB)
Data Offset : 8192 sectors
After I fixed the superblock:
Avail Dev Size : 5842894848 (2786.11 GiB 2991.56 GB)
Array Size : 8764342272 (8358.33 GiB 8974.69 GB)
Data Offset : 8192 sectors
> So you normally wouldn't be able to increase the data_offset from 5120 to
> 8192 unless you first reduced the --size of the array (having reduced the
> size of any filesystem first).
Well, it let me do it.
> Did you do that? That should have reduced sb->data_size appropriately.
No. I just went ahead and increased the data offset.
> If you did --grow the --size first, that should have reduced sb->data_size.
I did not do this step.
> If you didn't the --grow --data-offset should have failed.
I did this directly, and it let me. I had a slightly older kernel when
I started the reshape. 3.17.7 and mdadm 3.3.2.
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