CODEWITHSUNDEEP
mongodb
TasostheGreat
TasostheGreat

Reputation: 432

what happens when maxsize is exceeded

When the size of the cluster rises chunks are divided. Docs say that "the balancer will not move chunks off an overloaded shard. This must happen manually."(doc here). So will redudant chunks of a shard, that has reached the maxsize limit, be moved to another shard that hasn't exceeded the maxsize, or will they stay on the same shard and one must manually move those extra bytes and chunks off the shard?

Upvotes: 0

Views: 216

Answers (1)

Stennie
Stennie

Reputation: 65303

Docs say that "the balancer will not move chunks off an overloaded shard. This must happen manually.". So will redudant chunks of a shard, that has reached the maxsize limit, be moved to another shard that hasn't exceeded the maxsize, or will they stay on the same shard and one must manually move those extra bytes and chunks off the shard?

This is specific to when you have set maxSize limit for a shard and that limit has been reached. The balancer will no longer migrate chunks to that shard, and it will remain "full" unless you manually move some chunks to another shard via sh.moveChunk(). The default behaviour is to have no maxSize set so shards can use as much disk space as is available.

my scenario is that i have for example 2 servers one with a bigger hard drive than the other. So if one is 500GB and the other is 1TB and the first gets full with data, what happens when I add more data to the servers. Will the balancer know that the first is full and transfer the extra data from the first server to the second?

MongoDB balances data between shards on the basis of logical chunks that are contiguous ranges of values based on the shard key you have selected. By default a chunk represents roughly 64MB of data.

MongoDB is unaware of the underlying disk configuration, so if server with shardA has twice as much disk space as a server with shardB the balancer is still only considering the number of chunks associated with each shard (not the actual disk usage). Ideally all shards should have similar configuration in terms of hardware and disk space.

If you use the maxSize option to limit the storage on a specific shard, this setting only controls whether the balancer will move chunks to that shard once the maxSize has been reached.

For more information see Sharded Collection Balancing in the MongoDB documentation.

Upvotes: 1

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