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https://issues.apache.org/jira/browse/HDFS-17205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17772457#comment-17772457
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Ayush Saxena commented on HDFS-17205:
-------------------------------------
Committed to trunk.
Thanx [~haiyang Hu] for the contribution & [~hexiaoqiao] for the review!!!
> HdfsServerConstants.MIN_BLOCKS_FOR_WRITE should be configurable
> ---------------------------------------------------------------
>
> Key: HDFS-17205
> URL: https://issues.apache.org/jira/browse/HDFS-17205
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Haiyang Hu
> Assignee: Haiyang Hu
> Priority: Major
> Labels: pull-request-available
>
> Current allocate new block , the NameNode will choose datanode and choose a
> good storage of given storage type from datanode, the specific calling code
> is DatanodeDescriptor#chooseStorage4Block, here will calculate the space
> required for write operations,
> requiredSize = blockSize * HdfsServerConstants.MIN_BLOCKS_FOR_WRITE(default
> is 1).
> {code:java}
> public DatanodeStorageInfo chooseStorage4Block(StorageType t,
> long blockSize) {
> final long requiredSize =
> blockSize * HdfsServerConstants.MIN_BLOCKS_FOR_WRITE;
> final long scheduledSize = blockSize * getBlocksScheduled(t);
> long remaining = 0;
> DatanodeStorageInfo storage = null;
> for (DatanodeStorageInfo s : getStorageInfos()) {
> if (s.getState() == State.NORMAL && s.getStorageType() == t) {
> if (storage == null) {
> storage = s;
> }
> long r = s.getRemaining();
> if (r >= requiredSize) {
> remaining += r;
> }
> }
> }
> if (requiredSize > remaining - scheduledSize) {
> BlockPlacementPolicy.LOG.debug(
> "The node {} does not have enough {} space (required={},"
> + " scheduled={}, remaining={}).",
> this, t, requiredSize, scheduledSize, remaining);
> return null;
> }
> return storage;
> }
> {code}
> But when multiple NameSpaces select the storage of the same datanode to write
> blocks at the same time.
> In extreme cases, if there is only one block size left in the current
> storage, there will be a situation where there is not enough free space for
> the writer to write data.
> log similar to the following appears:
> {code:java}
> The volume [file:/disk1/] with the available space (=21129618 B) is less than
> the block size (=268435456 B).
> {code}
> In order to avoid this case, consider
> HdfsServerConstants.MIN_BLOCKS_FOR_WRITE should be configurable, and the
> parameters can be adjusted in larger clusters.
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