Great explanation!
Consider this scenario:
Given an MPI application which runs on a number of clients (more than one), and does some I/O operations.
Based on the explanation above, it looks like it is not possible to have multiple clients read or write to the same file at the same time when we have ceph block device mounted.
Therefore, the feasible option could be to mount CephFS over RBD for different clients to be able to do parallel I/O and take advantage of the features Ceph provides using RBD (striping for instance).
Does this sound correct?
Thanks,
Hadi
On Mon, Jul 6, 2015 at 1:28 PM, Scott Laird <scott@xxxxxxxxxxx> wrote:
CephFS is a filesystem, rbd is a block device. CephFS is a lot like NFS; it's a filesystem shared over the network where different machines can access it all at the same time. RBD is more like a hard disk image, shared over the network. It's easy to put a normal filesystem (like ext2) on top of it and mount it on a computer, but if you mount the same RBD device on multiple computers at once then Really Bad Things are going to happen to the filesystem.In general, if you want to share a bunch of files between multiple machines, then CephFS is your best bet. If you want to store a disk image, perhaps for use with virtual machines, then you want RBD. If you want storage that is mostly compatible with Amazon's S3, then use radosgw.On Mon, Jul 6, 2015 at 8:04 AM Hadi Montakhabi <hadi@xxxxxxxxx> wrote:_______________________________________________Hello Cephers,I can't quite grasp the difference between CephFS and Rados Block Device (RBD).In both cases we do mount the storage on the client and it is using the storage from the storage cluster.Would someone explain it to me like I am five please?Thanks,Hadi
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