[irods/irods#4103] Add dedicated section about quotas (4-3-stable)

docs/system_overview/quotas.md

@@ -0,0 +1,65 @@
+# Quota Enforcement
+
+iRODS offers two quota enforcement systems, [Physical Quotas](#physical-quotas) and [Logical Quotas](#logical-quotas).
+
+## Physical Quotas
+
+This system is for enforcing quotas at the physical layer (i.e. storage resources). Physical quotas _(sometimes referred to as resource quotas)_ are always associated with a specific group and one or more storage resources.
+
+### How to enable
+
+By default, physical quotas are disabled. To enable, open `/etc/irods/core.re` and change the argument passed to `msiSetRescQuotaPolicy()` from `"off"` to `"on"`. The line you modified should look very similar to the following.
+
+```py
+acRescQuotaPolicy { msiSetRescQuotaPolicy("on"); }
+```
+
+Reload the server's configuration for the change to take effect. This is currently a per-server setting. If your zone consists of multiple servers, make sure to apply the change to all of them.
+
+### Applying a Quota
+
+!!! Note
+    _User_ quotas are not supported by iRODS. However, they can be simulated through the use of _group_ quotas. See [Simulating User Quotas](../../administrators/policy_cookbook/#simulating-user-quotas) in the [Policy Cookbook](../../administrators/policy_cookbook) for more information.
+
+To apply a quota, all that's needed is a group.
+
+The following example sets a _group_ quota of 100000 bytes across all storage resources for the group named "quota_group".
+
+```sh
+iadmin sgq quota_group total 100000
+```
+
+The `total` keyword instructs iRODS to apply a global quota. Upon successfully setting the quota, all data associated with members of the "quota_group" will be counted toward the quota.
+
+To apply a quota to a specific storage resource, replace the `total` keyword with the name of the storage resource.
+
+See [iadmin sgq](../../icommands/administrator/#sgq) for more information.
+
+### Updating Quota Usage Totals
+
+Quota usage tracking is passive. iRODS does not auto-update quota usage totals as data changes. Administrators must run `iadmin cu` or invoke the necessary API to instruct iRODS to recalculate usage totals.
+
+The most common pattern for handling recalculation of quota usage totals is via a [cron](https://en.wikipedia.org/wiki/Cron) job.
+
+See [iadmin cu](../../icommands/administrator/#cu) for more information.
+
+### Viewing Quota Information
+
+Administrators can view quota information by running `iadmin lq`. `iquota` can be used to view quota information as well.
+
+See [iadmin lq](../../icommands/administrator/#lq) and [iquota](../../icommands/user/#iquota) for more information.
+
+## Logical Quotas
+
+This system is for enforcing quotas at the logical layer (i.e. collections and data objects). This is achieved through the use of the [Logical Quotas rule engine plugin](https://github.com/irods/irods_rule_engine_plugin_logical_quotas).
+
+See the [README](https://github.com/irods/irods_rule_engine_plugin_logical_quotas) in the GitHub repository for more information.
+
+## Related Links
+
+- [iadmin sgq](../../icommands/administrator/#sgq)
+- [iadmin cu](../../icommands/administrator/#cu)
+- [iadmin lq](../../icommands/administrator/#lq)
+- [iquota](../../icommands/user/#iquota)
+- [Logical Quotas rule engine plugin](https://github.com/irods/irods_rule_engine_plugin_logical_quotas)
+- [Policy Cookbook: Simulating User Quotas](../../administrators/policy_cookbook/#simulating-user-quotas)

mkdocs.yml

@@ -56,6 +56,7 @@ nav:
     - Configuration: 'system_overview/configuration.md'
     - SSL: 'system_overview/ssl.md'
     - Users and Permissions: 'system_overview/users_and_permissions.md'
+    - Quotas: 'system_overview/quotas.md'
     - GenQuery: 'system_overview/genquery.md'
     - Backing Up: 'system_overview/backing_up.md'
     - Federation: 'system_overview/federation.md'