Add information about writes on nearly full disks

[djwfyi]

MinIO Object Store can run into limitations when disk usage approaches nearly full usage.

Add information to /operations/install-deploy-manage/expand-minio-deployment.html#capacity-based-planning and/or on the deployment pages that drives >90% full are at risk of critical performance issues and require

• cleaning up old data
• adding a pool

Additional info about writes on highly used disks/pools:

• At >85% usage, writes are sent to pools with <85% usage when available
• At >99% usage, writes can no longer happen, though overwrites can happen

Note that MinIO requires more than the space of actual objects to be able to write bucket metadata, pool.bin info, and many other processes. MinIO requires that drives remain writable. Administrators should begin planning expansion when pool usage reaches 80% and have the new pools in place by the time the pool reaches 95%.

Verify the percentage assumptions above with engineers.

This information could also go on:

• operations/concepts/thresholds.html
• operations/checklists/hardware.html