[sheepdog-users] is --nohalt dangerous?
dietmar at proxmox.com
Wed Jul 18 08:15:12 CEST 2012
Wouldn't it be good enough if 2 out of 3 nodes are online?
> > The question is why that is not the default behavior? Is that dangerous?
> > If so, why?
> To quote from commit 9b6102ce:
> sheep: introduce SD_STATUS_HALT
> Currently, sheepdog will serve IO requests even if number of nodes is less
> than 'copies'.
> When the number of the nodes (or zones) is less than the copies specified
> by collie-cluster-format command, the sheepdog cluster should stop serving
> IO requests.
> This is necessary to solve the below subtle case:
> + good nodes, - failed nodes.
> 0 1 2 3
> + - - +
> + --> - --> - --> +
> + + - # <-- permanently down.
> this node has the latest data
> at stage 3, we will have a cluster recovered without the data tracked at
> stage 1.
> When the nodes are in the SD_STATUS_HALT, the sheepdog can also serve
> configuration change and do the recovery job.
More information about the sheepdog-users