Step 4 of 8 - Storage
Scaling without copying the data
One action, both lanes. The only difference is where the bytes already are.
Stateful nodes on EBS
100 GB to move
| Data to move | 200 ranges x 512 MB | 100 GB |
|---|---|---|
| Copy rate | rebalance snapshots are rate-limited per store | 32 MiB/s |
| Time to complete | 100 GB at 32 MiB/s, and the docs give a band of minutes to hours | 53 min |
| Consequence | can't shrink quickly, so provision for peak | peak-provisioned |
Stateless KV nodes, disaggregated storage
12 KB of metadata
| Hard links created | 200 ranges shared, not copied | 200 links |
|---|---|---|
| Metadata written | 200 x 64 bytes | 12 KB |
| Time to complete | 12 KB at 32 MiB/s | under a second |
| Bulk data moved | none: the range's SSTables are shared, not copied | 0 GB |
| Still sent | the range's store-local state, which no hard link shares | small |
How this is worked out
- Both bars run in real time. A second on screen is a second of the actual operation: the hard links are written in under a second and the copy needs 53 min, so the left-hand bar is still going when you leave the page. There's nothing to wait for.
-
Moving a range is rate-limited per store, so the duration is arithmetic:
100 GB at 32 MiB/s, which is
CockroachDB's default
kv.snapshot_rebalance.max_rate. It's the optimistic end - a real rebalance shares the link with your queries - and it lands inside the "minutes to hours" the design docs give.