[Linux-cluster] CLVM mirror implementation

Terry Burton tez at terryburton.co.uk
Fri Jul 25 10:46:27 UTC 2008


I find CLVM an appealing approach to providing storage to Xen hosts.
We can provide a single large SAN-backed LUN to all of our Xen hosts
which we manage using CLVM which allows us to raise a VM on any Xen
host and provide live migration between hosts.

However, the SAN does not support volume mirroring and is therefore a
single point of failure. I would like to move towards a HA solution
using some form of cluster-aware RAID. I have been investigating some
solutions for this and discovered Jonathan Brassows's report to the
Red Hat Cluster Summit (year?) entitled "LVM mirroring" [1] in which
he mentions the "cluster mirror implementation", presumably referring
to the ability of CLVM to support mirror LVs?

Following that line of thought I would like to present distinct LUNs
from two (or more) seperate SANs to all Xen Dom0 and configure these
as PVs belonging to a CLVM managed VG. I would then configure the LVs
that we present as storage to each Xen DomU using "lvcreate -m {1,2}
..." so that each VMs storage is provided from at least two SANs, each
of which can fail (or undergo maintainance) in isolation without loss
of service to the VMs.

Firstly, have I understood CLVM mirroring correctly in that it will
eventually support this scenario?

How close is CLVM mirroring to becoming a practical reality, including
the rapid detection of mirror failure (dmeventd) and automatic recover
of mirrors?

Thanks for your time,


[1] http://devresources.linux-foundation.org/dev/clusters/docs/cluster_summit_mirror_paper.pdf

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