Storage Classes in Ceph S3

❓ What?

Storage classes in [storage class](./ceph]] correspond to a certain data pool. They are a subsection of placement-rules-ceph-s3 that link them to data pools. A [[./storage-classes-ceph-s3) is unique to a placement rule but placement rules can have many storage classes. Every placement rule has a storage class called STANDARD by default but this STANDARD might correspond to different data pools for different placement rules.

Changing Default Storage Class for a User

The default storage class for a placement rule (and therefore a bucket) cannot be modified. If it’s desired that a certain user’s uploads, by default, goto a different storage class, this can be done by modifying the default_storage_class key for the specific user with radosgw-admin .

$ radosgw-admin user info --uid test-user
{
    "user_id": "test-user",
    "display_name": "test-user",
    "email": "",
    "suspended": 0,
    "max_buckets": 1000,
    "subusers": [],
    "keys": [
        {
            "user": "test-user",
            "access_key": "QTAQHWDZBLBSPAK3MEL3",
            "secret_key": "Oe9oqCDY1c3DIgqnK34CBo0M4IWyXkYtTP7MP3Yf"
        }
    ],
    "swift_keys": [],
    "caps": [],
    "op_mask": "read, write, delete",
    "default_placement": "",
    "default_storage_class": "",
    "placement_tags": [],
    "bucket_quota": {
        "enabled": false,
        "check_on_raw": false,
        "max_size": -1,
        "max_size_kb": 0,
        "max_objects": -1
    },
    "user_quota": {
        "enabled": false,
        "check_on_raw": false,
        "max_size": -1,
        "max_size_kb": 0,
        "max_objects": -1
    },
    "temp_url_keys": [],
    "type": "rgw",
    "mfa_ids": []
}
 
$ radosgw-admin user modify \
      --uid test-user \
      --placement-id default-placement \
      --storage-class hot_storage_class
{
    "user_id": "test-user",
    "display_name": "test-user",
    "email": "",
    "suspended": 0,
    "max_buckets": 1000,
    "subusers": [],
    "keys": [
        {
            "user": "test-user",
            "access_key": "QTAQHWDZBLBSPAK3MEL3",
            "secret_key": "Oe9oqCDY1c3DIgqnK34CBo0M4IWyXkYtTP7MP3Yf"
        }
    ],
    "swift_keys": [],
    "caps": [],
    "op_mask": "read, write, delete",
    "default_placement": "default-placement",
    "default_storage_class": "hot_storage_class",
    "placement_tags": [],
    "bucket_quota": {
        "enabled": false,
        "check_on_raw": false,
        "max_size": -1,
        "max_size_kb": 0,
        "max_objects": -1
    },
    "user_quota": {
        "enabled": false,
        "check_on_raw": false,
        "max_size": -1,
        "max_size_kb": 0,
        "max_objects": -1
    },
    "temp_url_keys": [],
    "type": "rgw",
    "mfa_ids": []
}

Otherwise, a storage class can also be specified during the time of the upload like in the placement rule example.

❔ Why?

Storage classes help users and administrators to prioritise space and costs by having different types of storage classes corresponding to different types of Device Class|device classes. For example, frequently accessed data may reside on NVMe while archives may reside on HDD. This type of Transitioning Data to a Different Storage Class|transitioning is made possible with Lifecycle Policy|lifecycle policies.

🎤 How?

A storage class can be created like so:

Same over the command line:

radosgw-admin zonegroup placement add \
      --rgw-zonegroup default \
      --placement-id default-placement \
      --storage-class hot_storage_class
 
radosgw-admin zone placement add \
      --rgw-zone default \
      --placement-id default-placement \
      --storage-class hot_storage_class \
      --data-pool hot.rgw.data \
      --compression lz4

👓 References

https://docs.ceph.com/en/latest/radosgw/placement/#adding-a-storage-class