sumitagrawl commented on code in PR #8388: URL: https://github.com/apache/ozone/pull/8388#discussion_r2083765877
########## hadoop-hdds/docs/content/design/dn-min-space-configuration.md: ########## @@ -0,0 +1,105 @@ +--- +title: Minimum free space configuration for datanode volumes +summary: Describe proposal for minimum free space configuration which volume must have to function correctly. +date: 2025-05-05 +jira: HDDS-12928 +status: implemented +author: Sumit Agrawal +--- +<!-- + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + http://www.apache.org/licenses/LICENSE-2.0 + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. See accompanying LICENSE file. +--> + +# Abstract +Volume in the datanode stores the container data and metadata (rocks db co-located on the volume). +There are various parallel operation going on such as import container, export container, write and delete data blocks, +container repairs, create and delete containers. The space is also required for volume db to perform compaction at regular interval. +This is hard to capture exact usages and free available space. So, this is required to configure minimum free space +so that datanode operation can perform without any corruption and environment being stuck and support read of data. + +This free space is used to ensure volume allocation if `required space < (volume available space - free space - reserved space)` +Any container creation and import container need ensure this constrain is met. And block write need ensure that this space is available if new blocks are written. +Note: Any issue related to ensuring free space is tracked with separate JIRA. + +# Existing configuration +Two configuration is provided, +- hdds.datanode.volume.min.free.space (default: 5GB) +- hdds.datanode.volume.min.free.space.percent + +1. If nothing is configured, takes default value as 5GB +2. if both are configured, priority to hdds.datanode.volume.min.free.space +3. else respective configuration is used. + +# Problem Statement + +- With 5GB default configuration, its not avoiding full disk scenario due to error in ensuring free space availability. +This is due to container size being imported is 5GB which is near boundary, and other parallel operation. +- Volume DB size can increase with increase in disk space as container and blocks it can hold can more and hence metadata. +- Volume DB size can also vary due to small files and big files combination, as more small files can lead to more metadata. + +Solution involves +- appropriate default min free space +- depends on disk size variation + +# Approach 1 Combination of minimum free space and percent increase on disk size + +Configuration: +1. Minimum free space: hdds.datanode.volume.min.free.space: default value `20GB` +2. disk size variation: hdds.datanode.volume.min.free.space.percent: default 0.1% or 0.001 ratio + +Minimum free space = Max (`<Min free space>`, `<percent disk space>`) + +| Disk space | Min Free Space (percent: 1%) | Min Free Space ( percent: 0.1%) | +| -- |------------------------------|---------------------------------| +| 100 GB | 20 GB | 20 GB (min space default) | +| 1 TB | 20 GB | 20 GB (min space default) | +| 10 TB | 100 GB | 20 GB (min space default) | +| 100 TB | 1 TB | 100 GB | + +considering above table with this solution, +- 0.1 % to be sufficient to hold almost all cases, as not observed any dn volume db to be more that 1-2 GB + +# Approach 2 Only minimum free space configuration + +Considering above approach, 20 GB as default should be sufficient for most of the disk, as usually disk size is 10-15TB as seen. +Higher disk is rarely used, and instead multiple volumes are attached to same DN with multiple disk. + +Considering this scenario, Minimum free space: `hdds.datanode.volume.min.free.space` itself is enough and +percent based configuration can be removed. + +### Compatibility +If `hdds.datanode.volume.min.free.space.percent` is configured, this should not have any impact +as default value is increased to 20GB which will consider most of the use case. + +# Approach 3 Combination of maximum free space and percent configuration on disk size + +Configuration: +1. Maximum free space: hdds.datanode.volume.min.free.space: default value `20GB` +2. disk size variation: hdds.datanode.volume.min.free.space.percent: default 10% or 0.1 ratio + +Minimum free space = **Min** (`<Max free space>`, `<percent disk space>`) +> Difference with approach `one` is, Min function over the 2 above configuration + +| Disk space | Min Free Space (20GB, 10% of disk) | +| -- |------------------------------------| +| 10 GB | 1 GB (=Min(20GB, 1GB) | +| 100 GB | 10 GB (=Min(20GB, 10GB) | +| 1 TB | 20 GB (=Min(20GB, 100GB) | +| 10 TB | 20 GB (=Min(20GB, 1TB) | +| 100 TB | 20GB (=Min(20GB, 10TB) | + +This case is more useful for test environment where disk space is less and no need any additional configuration. + +# Conclusion +1. Going with Approach 1 Review Comment: updated ########## hadoop-hdds/container-service/src/test/java/org/apache/hadoop/ozone/container/common/statemachine/TestDatanodeConfiguration.java: ########## @@ -199,10 +200,11 @@ void useMinFreeSpaceIfBothMinFreeSpacePropertiesSet() { DatanodeConfiguration subject = conf.getObject(DatanodeConfiguration.class); assertEquals(minFreeSpace, subject.getMinFreeSpace()); - assertEquals(DatanodeConfiguration.MIN_FREE_SPACE_UNSET, subject.getMinFreeSpaceRatio()); + assertEquals(.5f, subject.getMinFreeSpaceRatio()); Review Comment: updated ########## hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/statemachine/DatanodeConfiguration.java: ########## @@ -689,33 +690,14 @@ public void validate() { * else it will fall back to 'hdds.datanode.volume.min.free.space.default' */ private void validateMinFreeSpace() { - if (minFreeSpaceRatio > 1) { + if (minFreeSpaceRatio > 1 || minFreeSpaceRatio < 0) { Review Comment: updated -- This is an automated message from the Apache Git Service. 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