[sheepdog-users] cluster data distribution
sirio81 at gmail.com
Thu May 9 17:04:26 CEST 2013
2013/5/9 Liu Yuan <namei.unix at gmail.com>:
> Since we don't change weight by plugging/unplugging disks, there is no
> way to rebalance data. If we allow weight-change for plug/unplug, we
> have to pay price: plug/unplug one disk will trigger the whole cluster
Looking at it from the other side:
my node uses two disks: 2T + 500G.
What happens then if I unplug the 2T disk now? It contains lot's of data.
Data can't be distributed across the node disk.
It's has to trigger a cluster recover.
When I plug the disk backup, this node is not going to be used much.
root at sheepdog001:~# collie node md info
Id Size Use Path
0 1.2 TB 593 GB /mnt/ST2000DM001-1CH164_W1E2N5G6/obj
1 212 GB 253 GB /mnt/wd_WMAYP0904279
I do not like the idea of having more sheeps on a single node.
I think it's dangerous because n sheeps on a node may be bigger than n copies.
I the whole host dies, more nodes are going to die.
That's why I like md approach.
I think a recovery/rebalance is needed.
Maybe not automatically, but by a collie command, so we can choose to
trigger the cluster when it's less loaded.
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