Re: metadata management in case of ceph object storage and ceph block storage

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Hi,

Maybe others had your mail going into junk as well, but that is why at least I did not see  it.

To your question, which I’m not sure I understand completely.

In Ceph you have three distinct types of services,

Mon, Monitors
MDS, Metadata Servers
OSD, Object Storage Devices

And some other concepts

PG, placement group
Object
Pool

So a Pool contains PGs that contains Objects, in that order.
Monitors keeps track of pools and PGs, and the objects are kept on the OSD.

In case you’re running CephFS, the Ceph File System, you also have files, which the MDS keeps track of.

So yes, you don’t need the MDS if you just keep track of block storage and object storage. (i.e. images for KVM)

So the Mon keeps track of the metadata for the Pool and PG
and the MDS keep track of all the files, hence the MDS should have at least 10x the memory of what the Mon have.

I’m no Ceph expert, especially not on CephFS, but this is my picture of it :)

Maybe the architecture docs could help you out? http://docs.ceph.com/docs/master/architecture/#cluster-map

Hope that resolves your question.

Cheers,
Josef

On 06 Apr 2015, at 18:51, pragya jain <prag_2648@xxxxxxxxxxx> wrote:

Please somebody reply my queries.

Thank yuo
 
-----
Regards
Pragya Jain
Department of Computer Science
University of Delhi
Delhi, India



On Saturday, 4 April 2015 3:24 PM, pragya jain <prag_2648@xxxxxxxxxxx> wrote:


hello all!

As the documentation said "One of the unique features of Ceph is that it decouples data and metadata".
for applying the mechanism of decoupling, Ceph uses Metadata Server (MDS) cluster.
MDS cluster manages metadata operations, like open or rename a file

On the other hand, Ceph implementation for object storage as a service and block storage as a service does not require MDS implementation.

My question is:
In case of object storage and block storage, how does Ceph manage the metadata?

Please help me to understand this concept more clearly.

Thank you
 
-----
Regards
Pragya Jain
Department of Computer Science
University of Delhi
Delhi, India


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