krishnaasawa1 commented on code in PR #8388: URL: https://github.com/apache/ozone/pull/8388#discussion_r2073127863
########## hadoop-hdds/docs/content/design/dn-min-space-configuration.md: ########## @@ -0,0 +1,106 @@ +--- +title: Minimum free space configuration for datanode volumes +summary: Describe proposal for minimum free space configuration which volume must have to function correctly. +date: 2025-05-5 +jira: HDDS-12928 +status: draft +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 datanode stores the container data and metadata of this is present in volume db. +There are various parallel operation going on such as import container, export container, write and delete data blocks, +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 `10GB` +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 | 10 GB | 10 GB (min space default) | +| 1 TB | 10 GB | 10 GB (min space default) | +| 10 TB | 100 GB | 10 GB | +| 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, 10 GB as default should be sufficient for most of the disk, as usually disk size is 10-15TB as seen. Review Comment: Can the default value be in line with container size . Say a user change container size to 20 GB . Then default can be 2* container size . But let say someone use 1 GB then 2* container size may not suffice as volume DB can exceed. May be a default of -> container size + 5 GB (to cover volume DB) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
