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Cinder on Cloud VPS
This post explores the new Openstack Cinder feature for Cloud VPS.
By Andrew Bogott, Senior Site Reliability Engineer, The Wikimedia Foundation
We’ve just added a new, long-overdue feature to Cloud VPS: attachable block storage, aka Openstack Cinder
Historically, storage of large files and datasets has always been the weak link in the stack provided by Wikimedia Cloud Services. If you wanted to use disk space beyond the default 20Gb allocated for a new virtual machine, there were a few options—none of them ideal. If you wanted big, slow files (against a background of grumbling WMCS staff) you could use NFS. If you wanted more local storage you were limited to the available nova flavors; often choosing a large flavor meant using up your RAM or CPU quota when all you really wanted was a larger drive.
Starting in 2021 we’re offering Cinder as a third, better option. Cinder is a core OpenStack project that provides attachable storage, a standard feature in most public clouds. With Cinder you can create a standalone volume of arbitrary size, then attach that volume to a VM. When it comes time to rebuild a VM, you can detach the volume and re-attach it to a newer, upgraded VM. Better yet, Cinder volumes can be extended as they fill up.
Our hope is that Cinder will immediately replace some of the simpler NFS use cases. NFS is likely to remain state of the art for shared read-only use cases (e.g. dumps), but every time we can eliminate a read/write NFS share the rest of cloud-VPS works a little bit better for everyone.
If you’re making a new database, put it on a Cinder volume today! The old local-storage/LVM setup is still supported, but over the next few months, we hope to replace all existing automated uses of LVM so that we can standardize all nova flavors on a single 20Gb size and move all additional storage needs onto Cinder workflows.
Currently, each Cloud VPS project has a Cinder quota of 10Gb. Our plan is to be generous in granting quota requests in the short term. Eventually, we may settle on a higher default quota once we know more about how (and how much) our users are relying on this feature.
NFS: Shared volumes for dumps, scratch work, or shared cross-project storage
Local Storage + LVM: Extended storage partitioned from the primary instance volume
LVM partitions are local to the VM, so provide the same performance as any other local file access.
Puppet classes exist to support simple, consistent workflows.
Cinder: Attachable block storage managed with Horizon.
Some existing workflows (in particular, puppetized use cases) are not yet supported for Cinder. Transitioning from LVM to Ceph storage for existing projects may be cumbersome, requiring new puppet classes that somehow detect whether a VM is pre- or post-Cinder.
A Cinder volume can only be attached to one VM at a time. Shared storage is going to remain the exclusive domain of NFS for the foreseeable future.
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Cinder on Cloud VPS”
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