Re: CephFS object mapping.

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Hi,

On 5/22/19 5:53 PM, Robert LeBlanc wrote:
On Wed, May 22, 2019 at 12:22 AM Burkhard Linke <Burkhard.Linke@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi,

On 5/21/19 9:46 PM, Robert LeBlanc wrote:
> I'm at a new job working with Ceph again and am excited to back in the
> community!
>
> I can't find any documentation to support this, so please help me
> understand if I got this right.
>
> I've got a Jewel cluster with CephFS and we have an inconsistent PG.
> All copies of the object are zero size, but the digest says that it
> should be a non-zero size, so it seems that my two options are, delete
> the file that the object is part of, or rewrite the object with RADOS
> to update the digest. So, this leads to my question, how to I tell
> which file the object belongs to.
>
> From what I found, the object is prefixed with the hex value of the
> inode and suffixed by the stripe number:
> 1000d2ba15c.00000005
> <inode hex>.<hex stripe number>
>
> I then ran `find . -xdev -inum 1099732590940` and found a file on the
> CephFS file system. I just want to make sure that I found the right
> file before I start trying recovery options.
>

The first stripe XYZ.00000000 has some metadata stored as xattr (rados
xattr, not cephfs xattr). One of the entries has the key 'parent':

When you say 'some' is it a fixed offset that the file data starts? Is the first stripe just metadata?

No, the first stripe contains the first 4 MB of a file by default,. The xattr and omap data are stored separately.


Regards,

Burkhard


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