Re: Looking to Use Ceph

[Wido den Hollander <wido@widodh.nl>]

On 01/03/2013 01:29 PM, emyr.james wrote:
> Hi,
>
> I'm thinking of starting to use ceph initially for evaluation...seeing
> how it compares to our existing lustre file system.
> One thing that I would like confirmation of is how ceph stores large
> files. If I store a large file in CephFS is it automatically split up
> into chunks with the various chunks stored and replicated automatically
> across the whole cluster, or does it store the whole file as one object
> on one individial OSD and then has individual replicants of the whole
> file on a small number of other OSD's ? What is the typical block size
> used if files are split up....can this be configured ?
>

Files are by default striped in 4MB blocks which are then distributed 
over the OSDS and replicated.

A 1G file will thus result in 256 different object distributed and 
replicated through your cluster.

You can configure the stripe-size with the "cephfs" tool on a client.

Note: CephFS hasn't got the attention like RADOS and RBD got, so you 
might run into some weird situations.

Wido

> Regards,
>
> Emyr
>
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