Hi Jon, I already mentioned multiple times here - RBD just a block device. You can map it to multiple hosts, but before doing dd if=/dev/zero of=/media/tmp/test you have created file system, right? This file system MUST be distributed, thus multiple hosts can read and write files on it.
On Wed, May 29, 2013 at 4:24 AM, Jon <three1...@gmail.com> wrote: > Hello, > > I would like to mount a single RBD on multiple hosts to be able to share > the block device. > Is this possible? I understand that it's not possible to share data > between the different interfaces, e.g. CephFS and RBDs, but I don't see > anywhere it's declared that sharing an RBD between hosts is or is not > possible. > > I have followed the instructions on the github page of ceph-deploy (I was > following the 5 minute quick start > http://ceph.com/docs/next/start/quick-start/ but when I got to the step > with mkcephfs it erred out and pointed me to the github page), as I only > have three servers I am running the osds and monitors on all of the hosts, > I realize this isn't ideal but I'm hoping it will work for testing purposes. > > This is what my cluster looks like: > > >> root@red6:~# ceph -s > >> health HEALTH_OK > >> monmap e2: 3 mons at {kitt= > 192.168.0.35:6789/0,red6=192.168.0.40:6789/0,shepard=192.168.0.2:6789/0}, > election epoch 10, quorum 0,1,2 kitt,red6,shepard > >> osdmap e29: 5 osds: 5 up, 5 in > >> pgmap v1692: 192 pgs: 192 active+clean; 19935 MB data, 40441 MB > used, 2581 GB / 2620 GB avail; 73B/s rd, 0op/s > >> mdsmap e1: 0/0/1 up > > To test, what I have done is created a 20GB RBD mapped it and mounted it > to /media/tmp on all the hosts in my cluster, so all of the hosts are also > clients. > > Then I use dd to create a 1MB file named test-$hostname > > >> dd if=/dev/zero of=/media/tmp/test-`hostname` bs=1024 count=1024; > > after the file is created, I wait for the writes to finish in `ceph -w`, > then on each host when I list /media/tmp I see the results of > /media/tmp/test-`hostname`, if I unmount then remount the RBD, I get mixed > results. Typically, I see the file that was created on the host that is at > the front of the line in the quorum. e.g. the test I did while typing this > e-mail "kitt" is listed first quorum 0,1,2 kitt,red6,shepard, this is the > file I see created when I unmount then mount the rbd on shepard. > > Where this is going is, I would like to use CEPH as my back end storage > solution for my virtualization cluster. The general idea is the > hypervisors will all have a shared mountpoint that holds images and vms so > vms can easily be migrated between hypervisors. Actually, I was thinking I > would create one mountpoint each for images and vms for performance > reasons, am I likely to see performance gains using more smaller RBDs vs > fewer larger RBDs? > > Thanks for any feedback, > Jon A > > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- Igor Laskovy facebook.com/igor.laskovy studiogrizzly.com
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