Thanks Arpit Agarwal for adding document for this. That will be very helpful for people to understand and use this feature.
Patch looks good to me overall. In addition to Brahma Reddy Battula's comments, I just have a few minor issues.
"The DataNodes" -> The DataNode
1. "Rare data loss is possible in the event of a node restart or a network partition."
-> Rare data loss is possible in the event of a data node restart *before replicas are persisted to disk*.
"network partition" in here is not very clear, maybe we can remove it.
2. "Applications that use Lazy Persist writes"
-> "Lazy Persist Writes" should be used consistently.
3. "Applications that use Lazy Persist writes will work when there is insufficient memory or when the feature is not configured by the administrator. HDFS will transparently use hard disk storage for writes when memory is unavailable or not configured."
-> Can you elaborate "when the feature is not configured by the administrator"? Or we can say, this feature will continue to work by automatically fallback to DISK storage for write if memory is insufficient, unavailable or not configured.
4. ",the "locked-in-memory size" ulimit (`ulimit -l`) of the Data Node user also needs to be increased to match this parameter (see the related section on [OS Limits]"
->"Data Node user", do you mean hdfs super user or the Data Node?
5. "Using more than one `tmpfs` partition per Data Node for Lazy Persist writes is not recommended."
-> Lazy Persist Writes
6. "This step is crucial. You will lose data if a `tmpfs` mount is not correctly tagged as RAM_DISK."
-> Can you elaborate more on this? For example, "Without RAM_DISK tag, the volatile storage will be treated as DISK without lazy persist. Data will be lost upon Data Node restart."
I tried to apply the patch and check the rendered new sites but git apply --binary always failed. Do I miss anything?
$ git apply --binary
error: cannot apply binary patch to 'hadoop-hdfs-project/hadoop-hdfs/src/site/resources/images/LazyPersistWrites.png' without full index line
error: hadoop-hdfs-project/hadoop-hdfs/src/site/resources/images/LazyPersistWrites.png: patch does not apply