Hi, 1. I found in the "Logical Volume Manager Administration" manual for RHEL 6 on p.12 and on p.35 the following statement:
"LVM snapshots are not supported across the nodes in a cluster. You cannot create a snapshot volume in a clustered volume group." I understand that this means no snapshots for shared volumes when using CLVM. 2. Strangely enough, I also found the following fragment on p.4 of the same manual: "If you are using a clustered system for failover where only a single node that accesses the storage is active at any one time, you should use High Availability Logical Volume Manager agents (HA-LVM). For information on HA-LVM, see Configuring and Managing a Red Hat Cluster." I understand this as an older system of synchronizing LVM configuration across the nodes that predates CLVM. I thought it was deprecated. Anyway, I cannot find any pointers to it in the current RHEL 6 manual. Questions: - Is HA-LVM still a viable option for the "one at a time" scenario described in the fragment above? - If so, where do I find more information about HA-LVM? What should I search for? - If it is still a viable option, would it support LVM snapshots? Thanks and regards, Chris Jankowski -----Original Message----- From: Jankowski, Chris Sent: Wednesday, 24 November 2010 07:23 To: 'linux clustering' Subject: RE: [Linux-cluster] RHEL 6 cluster filesystem resource and LVM snapshots Roger, Thank you. I see your point. Indeed, it looks that I need CLVM regardless of the type of filesystem used. Question: Does CLSVM support snapshots? Thanks and regards, Chris Jankowski -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Roger Pena Escobio Sent: Wednesday, 24 November 2010 01:32 To: linux clustering Subject: Re: [Linux-cluster] RHEL 6 cluster filesystem resource and LVM snapshots --- On Tue, 11/23/10, Jankowski, Chris <[email protected]> wrote: > From: Jankowski, Chris <[email protected]> > Subject: Re: [Linux-cluster] RHEL 6 cluster filesystem resource and LVM > snapshots > To: "linux clustering" <[email protected]> > Received: Tuesday, November 23, 2010, 6:45 AM > Xavier, > > I do not think that I have to use CLVM with ext4 or XFS in > a cluster. > > The ext4 or XFS filesystems will be on shared (FC) storage, > but they will be presented as a filesystem resource i.e. > accessible to only one cluster at a time, as they have to > be. So, I believe that simple LVM will do and snapshots will > be available. Hi Chris first I would like to say it has been a long time since I used RHCS and the only major problems I had was with clvm, but, by your question, I think if you still foresee changes in the lvm space, you will still need clvm, even if the filesystem will be a non-cluster FS the lvm layout is independent of the filesystem used, you might want to add more volumes to a group, resize, etc, and that info is read and cached when the kernel read the device, not when mounting the filesyste, so, if the device is presented to a node of the cluster, it will read the lvm layout and filesystem properties, even if not mounted. If you change that layout in one node, the others nodes might have a wrong information that could led to a crash in case you tried to mount the fs in there. see the point of having clvm in a cluster even if using ext3/4 ? if you don't plan to use lvm for the cluster, which is possible since you are having the device from a SAN/NAS/iSCSI where you will have exactly, or almost exactly, the same features that LVM provide, why having the extra layer if you will not use it ? that is the conclusion I reached years ago when facing problems with CLVM thanks roger -- Linux-cluster mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-cluster -- Linux-cluster mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-cluster
