elek commented on a change in pull request #1419:
URL: https://github.com/apache/hadoop-ozone/pull/1419#discussion_r492104772
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File path: hadoop-hdds/docs/content/design/storage-class.md
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@@ -19,10 +19,331 @@ author: Marton Ele
See the License for the specific language governing permissions and
limitations under the License. See accompanying LICENSE file.
-->
+
+
# Abstract
-Proposal suggest to introduce a new storage-class abstraction which can be
used to define different replication strategies (factor, type, ...) for
different bucket/keys.
+One of the fundamental abstraction of Ozone is the _Container_ which used as
the unit of the replication.
+
+Containers have to favors: _Open_ and _Closed_ containers: Open containers are
replicated by Ratis and writable, Closed containers are replicated with data
copy and read only.
+
+In this document a new level of abstraction is proposed: the *storage class*
which defines which type of containers should be used and what type of
transitions are supported.
+
+# Goals / Use cases
+
+## [USER] Simplify user interface and improve usability
+
+Users can choose from an admin provided set of storage classes (for example
`STANDARD`, `REDUCED`) instead of using implementation specific terms
(`RATIS/THREE`, `RATIS/ONE`)
+
+Today the users should use implementation spefific terms when key is created:
+
+```
+ozone sh key put --replication=THREE --type=RATIS /vol1/bucket1/key1
source-file.txt
+```
+
+There are two problems here:
+
+ 1. User should use low-level, technical terms during the usage. User might
not know what is `RATIS` and may not have enough information to decide the
right replication scheme.
+
+ 2. The current keys are only for the *open* containers. There is no easy way
to add configuration which can be used later during the lifecycle of
containers/keys. (For example to support `Ratis/THREE` --> `Ratis/TWO`)
+
+With the storage-class abstraction the complexity of configuration can be
moved to the admin side (with more flexibility). And user should choose only
from the available storage-classes (or use the default one).
+
+Instead of the earlier CLI this document proposes to use an abstract
storage-class parameter instead:
+
+```
+ozone sh key put --storage-class=STANDARD /vol1/bucket1/key1 source-file.txt
+```
+
+## [USER] Set a custom replication for a newly created bucket
+
+A user may want to set a custom replication for bucket at the time of
creation. All keys in the bucket will respect the specified storage class
(subject to storage and quota availability). E.g.
+
+```
+ozone sh bucket create --storage-class=INFREQUENT_ACCESS
+```
+
+
+Bucket-level default storage-class can be overridden for ay key, but will be
used as default.
+
+
+## [USER] Fine grained replication control when using S3 API
+
+A user may want to set custom replication policies for any key **which
uploaded via S3 API**. Storage-classes are already used by AWS S3 API. With
first-class support of the same concept in Ozone users can choose from the
predefined storage-classes (=replication rules) with using AWS API:
+
+
+```
+aws s3 cp --storage-class=REDUCED file1 s3://bucket/file1
+```
+
+
+## [USER] Set the replication for a specific prefix
+
+A user may want to set a custom replication for a specific key prefix. All
keys matching that prefix will respect the specified storage class. This
operation will not affect keys already in the prefix (question: consider
supporting this with data movement?)
+
Review comment:
Good question. storage-class is assigned to containers and keys, so keys
already have storage-classes, but might be the default. To start with I think
we should enable to set default storage class only when the prefix/bucket is
created.
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