On 09/14/2017 11:17 AM, Ronny Aasen wrote:
On 14. sep. 2017 00:34, James Okken wrote:
Thanks Ronny! Exactly the info I need. And kinda of what I thought the answer
would be as I was typing and thinking clearer about what I was asking. I just
was hoping CEPH would work like this since the openstack fuel tools deploy
CEPH storage nodes easily.
I agree I would not be using CEPH for its strengths.
I am interested further in what you've said in this paragraph though:
"if you want to have FC SAN attached storage on servers, shareable
between servers in a usable fashion I would rather mount the same SAN
lun on multiple servers and use a cluster filesystem like ocfs or gfs
that is made for this kind of solution."
Please allow me to ask you a few questions regarding that even though it
isn't CEPH specific.
Do you mean gfs/gfs2 global file system?
Does ocfs and/or gfs require some sort of management/clustering server to
maintain and manage? (akin to a CEPH OSD)
I'd love to find a distributed/cluster filesystem where I can just partition
and format. And then be able to mount and use that same SAN datastore from
multiple servers without a management server.
If ocfs or gfs do need a server of this sort does it needed to be involved in
the I/O? or will I be able to mount the datastore, similar to any other disk
and the IO goes across the fiberchannel?
i only have experience with ocfs. but i think gfs works similarish. There are
quite a few cluster filesystems to choose from.
https://en.wikipedia.org/wiki/Clustered_file_system
servers that are mounting ocfs shared filesystems must have ocfs2-tools
installed. have access to the common shared FC lun via FC. they need to be
aware of the other ocfs servers of the same lun, that you define in a
/etc/ocfs/cluster.conf configfile and the ocfs daemon must be running.
then it is just a matter of making the ocfs (on one server) and adding it to
fstab (of all servers) and mount.
One final question, if you don't mind, do you think I could use ext4or xfs
and "mount the same SAN lun on multiple servers" if I can guarantee each
server will only right to its own specific directory and never anywhere the
other servers will be writing? (I even have the SAN mapped to each server
using different lun's)
mounting the same (non cluster) filesystem on multiple servers is guaranteed
to destroy the filesystem, you will have multiple servers writing in the same
metadata area, the same journal area and generaly shitting over each other.
luckily i think most modern filesystems would detect that the FS is mounted
somewhere else and prevent you from mounting it again without big fat warnings.
kind regards
Ronny Aasen
In general, you can get shared file systems (i.e., the clients can all see the
same files and directories) with lots of different approaches:
* use a shared disk file system like GFS2, OCFS2 - all of the "clients" where
the applications run are part of the cluster and each server attaches to the
shared storage (through iSCSI, FC, whatever). They do require HA cluster
infrastructure for things like fencing
* use a distributed file system like cephfs, glusterfs, etc - your clients
access through a file system specific protocol, they don't see raw storage
* take any file system (local or other) and re-export it as a client/server type
of file system by using an NFS server or Samba server
Ric
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