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https://issues.apache.org/jira/browse/HDFS-13863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594766#comment-16594766
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Fei Hui commented on HDFS-13863:
--------------------------------
[~linyiqun] Thanks for you comments.
Two cases with DiskOutOfSpaceException：
* No more available volumes
* Out of space: "+ "The volume with the most available space (=" + maxAvailable
+ " B) is less than the block size (=" + blockSize + " B).
Maybe the exception message could make us understand why fall back to
persistent storage ?
> FsDatasetImpl should log DiskOutOfSpaceException
> ------------------------------------------------
>
> Key: HDFS-13863
> URL: https://issues.apache.org/jira/browse/HDFS-13863
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 3.1.0, 2.9.1, 3.0.3
> Reporter: Fei Hui
> Assignee: Fei Hui
> Priority: Major
> Attachments: HDFS-13863.001.patch, HDFS-13863.002.patch
>
>
> The code in function *createRbw* as follow
> {code:java}
> try {
> // First try to place the block on a transient volume.
> ref = volumes.getNextTransientVolume(b.getNumBytes());
> datanode.getMetrics().incrRamDiskBlocksWrite();
> } catch (DiskOutOfSpaceException de) {
> // Ignore the exception since we just fall back to persistent
> storage.
> } finally {
> if (ref == null) {
> cacheManager.release(b.getNumBytes());
> }
> }
> {code}
> I think we should log the exception because it took me long time to resolve
> problems, and maybe others face the same problems.
> When i test ram_disk, i found no data was written into randomdisk. I debug,
> deep into the source code, and found that randomdisk size was less than
> reserved space. I think if message was logged, i would resolve the problem
> quickly.
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