topic Re: lvm configuration in Operating System - Linux

lvm configuration

ats1 — Sat, 02 Apr 2011 16:39:24 GMT

Hi all,

I used LVM to configure a shared disk array (MSAP2000). But when I create a file on the shared disk from noeud1 (linux redhat 5), I do not see the same file from the second node.

i need some assistance please

Re: lvm configuration

ats1 — Sat, 02 Apr 2011 16:47:30 GMT

i use ext3 on the shared disk

Re: lvm configuration

Julio Yamawaki — Sat, 02 Apr 2011 22:42:11 GMT

Hi, I think you need some software like GFS in order to see these shared disk in both nodes.

Regards.

Re: lvm configuration

Matti_Kurkela — Sun, 03 Apr 2011 09:29:16 GMT

Node 2 has already read the directory information to its disk cache. When you use ext3 (or any other non-cluster filesystem), there is no way for node 1 to inform node 2 that it has made updates to the disk, so node 2 assumes its cached data is still valid. But it really isn't.

All the non-cluster filesystems have a very strong designed-in assumption that the filesystem is only mounted on *one node at a time* only.

MK

Re: lvm configuration

Ross Minkov — Sun, 03 Apr 2011 12:28:59 GMT

Hello ats1,

Red Hat GFS allows a cluster of Linux servers to share data in a common pool of storage -- see http://www.redhat.com/gfs/. The Cluster Logical Volume Manager (CLVM) provides a cluster-wide version of LVM2. CLVM provides the same capabilities as LVM2 on a single node, but makes the volumes available to all nodes in a Red Hat cluster. The logical volumes created with CLVM make logical volumes available to all nodes in a cluster. See https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Cluster_Suite_Overview/s1-clvm-overview-CSO.html.

HTH,
Ross

Re: lvm configuration

ats1 — Sun, 03 Apr 2011 15:03:13 GMT

the customer says, he has already clster with ext3. how can i enable the cache under LVM? Is not a problem with the preferred path?

Re: lvm configuration

macosta — Sun, 03 Apr 2011 17:53:26 GMT

The ext3 filesystem is not cluster-aware. If you have it mounted read-write on multiple nodes at once, you will see corruption in the filesystem and if it's mounted read-only on one or more, there's no cache invalidation method to allow coherency.

You might get away with a failover config, where it is mounted on one node, and upon some sort of failover, it's activated and mounted on another node - this is left as an exercise for the reader.

If you need an active-active mount, you need a cluster aware filesystem, such as GFS (see the information posted by others above - they've already answered your questions.

Re: lvm configuration

Patrick Terlisten — Sun, 03 Apr 2011 19:36:53 GMT

Hello,

sure you customer can use EXT3 within a cluster... but only one node can mount it at a given time. So in case of a failover, the filesystem is re-mounted on the failover node. EXT3 can't be accessed by more then one node at the same time. That's impossible. Use a cluster-aware filesystem like Oracle OCFS2 or GFS.

Regards,
Patrick

Re: lvm configuration

Reiner Rottmann — Mon, 04 Apr 2011 06:07:58 GMT

If you need readonly access and the data does not change very often, you may also create a LVM snapshot of the volume and mount it on the other node.

If you don't want to use a cluster filesystem, you may also sync two volumes via rsync or DRBD (distributed redundant block device: think of RAID1 via LAN)

Usually you can't open a LVM volume on multiple devices as the volume will get locked on the first mount.

Not only the filesystem needs to be clusteraware but also the volume manager. Use clvmd that is part of the Red Hat cluster suite.

Re: lvm configuration

ats1 — Tue, 05 Apr 2011 09:17:02 GMT

Hi all,

Can you give me a script to mount and dismount files system. How can i setup those scripts?

bests regards

Ats1