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lvm configuration

 
ats1
Frequent Advisor

lvm configuration


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
9 REPLIES
ats1
Frequent Advisor

Re: lvm configuration

i use ext3 on the shared disk
Julio Yamawaki
Esteemed Contributor

Re: lvm configuration

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

Regards.
Matti_Kurkela
Honored Contributor

Re: lvm configuration

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
MK
Ross Minkov
Esteemed Contributor

Re: lvm configuration

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
ats1
Frequent Advisor

Re: lvm configuration

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?
macosta
Trusted Contributor

Re: lvm configuration

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.
Patrick Terlisten
Honored Contributor

Re: lvm configuration

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
Best regards,
Patrick
Reiner Rottmann
Frequent Advisor

Re: lvm configuration

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.
ats1
Frequent Advisor

Re: lvm configuration

Hi all,

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

bests regards

Ats1