As Jan has already mentioned, Ceph and Cassandra do almost all of the same things. "Replicated self healing data storage on commodity hardware without a SPOF" describes both of these systems. If you did manage to get it running it would be a nightmare to reason about what's happening at the disk and network level.
You're going to get write amplification by your replication factor of both Cassandra, and Ceph unless you turn one of them down. This impacts disk I/O, disk space, CPU, and network bandwidth. If you turned down Ceph replication I think it would be possible for all of the replicated data for some chunk to be stored on one node and be at risk of loss. E.g. 1x Ceph, 3x Cassandra replication could store all 3 Cassandra replicas on the same Ceph node. 3x Ceph, 1x Cassandra would be safer, but presumably slower. Lastly Cassandra is designed around running against local disks, you will lose a lot of the advantages of this running it on Ceph. Daniel. On Mon, 2 Feb 2015 at 1:11 am Baskar Duraikannu < baskar.duraika...@outlook.com> wrote: > What is the reason for running Cassandra on Ceph? I have both running in > my environment but doing different things - Cassandra as transactional > store and Ceph as block storage for storing files. > ------------------------------ > From: Jan <cne...@yahoo.com> > Sent: 2/1/2015 2:53 AM > To: user@cassandra.apache.org > Subject: Re: Cassandra on Ceph > > Colin; > > Ceph is a block based storage architecture based on RADOS. > It comes with its own replication & rebalancing along with a map of the > storage layer. > > Some more details & similarities: > a)Ceph stores a client’s data as objects within storage pools. (think > of C* partitions) > b) Using the CRUSH algorithm, Ceph calculates which placement group > should contain the object, (C* primary keys & vnode data distribution) > c) and further calculates which Ceph OSD Daemon should store the > placement group (C* node locality) > d) The CRUSH algorithm enables the Ceph Storage Cluster to scale, > rebalance, and recover dynamically (C* big table storage architecture). > > Summary: > C* comes with everything that Ceph provides (with the exception of block > storage). > There is no value add that Ceph brings to the table that C* does not > already provide. > I seriously doubt if C* could even work out of the box with yet another > level of replication & rebalancing. > > Hope this helps > Jan/ > > C* Architect > > > > > > > On Saturday, January 31, 2015 7:28 PM, Colin Taylor < > colin.tay...@gmail.com> wrote: > > > I may be forced to run Cassandra on top of Ceph. Does anyone have > experience / tips with this. Or alternatively, strong reasons why this > won't work. > > cheers > Colin > > >
