"minimum backup" in vnodes

[Carl Mueller <ca...@smartthings.com.INVALID>]

Goal: backup a cluster with the minimum amount of data. Restore to be done
with sstableloader

Let's start with a basic case:
- six node cluster
- one datacenter
- RF3
- data is perfectly replicated/repaired
- Manual tokens (no vnodes)
- simplest strategy

In this case, it is (theoretically) possible to get an perfect backup of
data by storing the snapshots of two of the six nodes in the cluster due to
replication factor.

I once tried to parse the ring output with vnodes (256) and came to the
conclusion that it was not possible with vnodes, maybe you could avoid one
or two nodes of the six... tops. But I may have had an incorrect
understanding of how ranges are replicated in vnodes.

Would it be possible to pick only two nodes out of a six node cluster with
vnodes and RF-3 that will backup the cluster?

Re: "minimum backup" in vnodes

[Elliott Sims <el...@backblaze.com>]

Assuming this isn't an existing cluster, the easiest method is probably to
use logical "racks" to explicitly control which hosts have a full replica
of the data.  with RF3 and 3 "racks", each "rack" has one complete replica.
If you're not using the logical racks, I think the replicas are spread
randomly and you can't generally reduce your backup count safely even with
a lot of work.

On Wed, Aug 15, 2018 at 1:39 PM, Carl Mueller <
carl.mueller@smartthings.com.invalid> wrote:

> Goal: backup a cluster with the minimum amount of data. Restore to be done
> with sstableloader
>
> Let's start with a basic case:
> - six node cluster
> - one datacenter
> - RF3
> - data is perfectly replicated/repaired
> - Manual tokens (no vnodes)
> - simplest strategy
>
> In this case, it is (theoretically) possible to get an perfect backup of
> data by storing the snapshots of two of the six nodes in the cluster due to
> replication factor.
>
> I once tried to parse the ring output with vnodes (256) and came to the
> conclusion that it was not possible with vnodes, maybe you could avoid one
> or two nodes of the six... tops. But I may have had an incorrect
> understanding of how ranges are replicated in vnodes.
>
> Would it be possible to pick only two nodes out of a six node cluster with
> vnodes and RF-3 that will backup the cluster?
>
>