Open Stack

In our environments, we offer two types of storage. Tenants can either use Ceph/RBD and trade speed/latency for reliability and protection against physical disk failures, or they can launch instances that are realized as LVs on an LVM VG that we create on top of a RAID 0 spanning all but the OS disk on the hypervisor. This lets the users elect to go all-in on speed and sacrifice reliability for applications where replication/HA is handled at the app level, if the data on the instance is sourced from elsewhere, or if they just don't care much about the data.

There are some further changes to our approach that we would like to make down the road, but in general our users seem to like the current system and being able to forgo reliability or speed as their circumstances demand.

From: joe at topjian.net 
Subject: Re: [Openstack-operators] RAID / stripe block storage volumes

Hi Robert,

Can you elaborate on "multiple underlying storage services"?

The reason I asked the initial question is because historically we've made our block storage service resilient to failure. Historically we also made our compute environment resilient to failure, too, but over time, we've seen users become more educated to cope with compute failure. As a result, we've been able to become more lenient with regard to building resilient compute environments.

We've been discussing how possible it would be to translate that same idea to block storage. Rather than have a large HA storage cluster (whether Ceph, Gluster, NetApp, etc), is it possible to offer simple single LVM volume servers and push the failure handling on to the user? 

Of course, this doesn't work for all types of use cases and environments. We still have projects which require the cloud to own most responsibility for failure than the users. 

But for environments were we offer general purpose / best effort compute and storage, what methods are available to help the user be resilient to block storage failures?

Joe

On Mon, Feb 8, 2016 at 12:09 PM, Robert Starmer <robert at kumul.us> wrote:

I've always recommended providing multiple underlying storage services to provide this rather than adding the overhead to the VM.  So, not in any of my systems or any I've worked with.

R


On Fri, Feb 5, 2016 at 5:56 PM, Joe Topjian <joe at topjian.net> wrote:

Hello,

Does anyone have users RAID'ing or striping multiple block storage volumes from within an instance?

If so, what was the experience? Good, bad, possible but with caveats?

Thanks,
Joe 
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