2014-06-18 1:28 GMT+08:00 Gregory Farnum <g...@inktank.com>:
> On Tue, Jun 17, 2014 at 3:22 AM, Ke-fei Lin <k...@kfei.net> wrote:
>> Hi list,
>>
>> How does RADOS check an object and its replica are consistent? Is there
>> a checksum in object's metadata or some other mechanisms? Does the
>> mechanism depend on OSD's underlying file system?
>
> It does not check consistency on read. On scrub it compares the local
> FS metadata (size et al) and RADOS metadata (object versions and
> things); on deep scrub it computes a checksum of each replica and
> compares them.
Thank you Greg.
Let's say if there are an object A and its replica B. On deep scrubbing RADOS
find that two objects have different checksums. How does RADOS determine
and repair the corrupted object?
> RADOS does not maintain checksums alongside the objects in replicated pools.
>
>> And what would happen if a corrupted object being readed (like a
>> corrupted block in traditional file system)?
>
> If the local filesystem doesn't return an error, it will return the
> data it was given to the end user. (btrfs maintains its own checksums
This sounds kind of dangerous. I think corrupted objects will be normal instead
of exception because we usually build up Ceph cluster by commodity hardware.
> and will return errors, but unfortunately xfs will not.)
And it seems there are lots of people still using XFS...
By the way, is this the main reason that Ceph officially suggests btrfs?
> -Greg
> Software Engineer #42 @ http://inktank.com | http://ceph.com
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