Thanks to all for your reply
It is clear that Monitor keeps track of Pools and PGs in the cluster and there
is no need of MDS for Ceph object storage and block storage, since both of
these storage types do not require to maintain a file hierarchy.But, I have a
question:In Ceph Object Storage, If we use Swift APIs to store objects, then
objects are stored in some container within an account according to user
interface. but in backend, objects are stored in PGs within a pool.Then, from
user perspective, there is a need to maintain the information about number of
objects stored in a container and number of container in an account etc. and
this information is needed to be updated timely as there are any changes in the
count.
How does Ceph maintain all these information?
Please reply. -----RegardsPragya JainDepartment of Computer ScienceUniversity
of DelhiDelhi, India
On Saturday, 18 April 2015 9:16 AM, pragya jain <[email protected]>
wrote:
Thanks to all for your reply -----RegardsPragya JainDepartment of Computer
ScienceUniversity of DelhiDelhi, India
On Friday, 17 April 2015 4:36 PM, Steffen W Sørensen <[email protected]> wrote:
On 17/04/2015, at 07.33, Josef Johansson <[email protected]> wrote:
To your question, which I’m not sure I understand completely.
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
Well there really ain’t no metadata at all as with a traditional File System,
monitors keep track of status of OSDs. Client compute which OSDs to go talk to
to get to wanted objects. thus no need for central meta data service to tell
clients where data are stored. Ceph is a distributed object storage system with
potential no SPF and ability to scale out.Try studying Ross’ slides f.ex.
here:http://www.slideshare.net/buildacloud/ceph-intro-and-architectural-overview-by-ross-turkor
many other good intros on the net, youtube etc.
Clients of a Ceph Cluster can access ‘objects’ (blobs with data) through
several means, programatic with librados, as virtual block devices through
librbd+librados, and finally as a S3 service through rados GW over http[s] the
meta data (users + ACLs, buckets+data…) for S3 objects are stored in various
pools in Ceph.
CephFS built on top of a Ceph object store can best be compared with
combination of a POSIX File System and other Networked File Systems f.ex.
NFS,CiFS, AFP, only with a different protocol + access mean (FUSE daemon or
kernel module). As it implements a regular file name space, it needs to store
meta data of which files exist in such a name space, this is the job of the MDS
server(s) which of course uses Ceph object store pools to persistent store this
file system meta data info
and the MDS keep track of all the files, hence the MDS should have at least 10x
the memory of what the Mon have.
Hmm 10x memory isn’t a rule of thumb in my book, it all depends of use case at
hand.MDS tracks meta data of files stored in a CephFS, which usually is far
from all data of a cluster unless CephFS is the only usage of course :)Many use
Ceph for sharing virtual block devices among multiple Hypervisors as disk
devices for virtual machines (VM images), f.ex. with Openstack, Proxmox etc.
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 <[email protected]> wrote:
Please somebody reply my queries.
Thank yuo -----RegardsPragya JainDepartment of Computer ScienceUniversity of
DelhiDelhi, India
On Saturday, 4 April 2015 3:24 PM, pragya jain <[email protected]>
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 -----RegardsPragya JainDepartment of Computer ScienceUniversity of
DelhiDelhi, India
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