[HDFS-11752] getNonDfsUsed return 0 if reserved bigger than actualNonDfsUsed

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 2.7.1
• Fix Version/s: 2.7.1
• Component/s: datanode, hdfs
• Labels: datanode hdfs
• Target Version/s: 2.7.1, 3.0.0-beta1
• Assignee: Unassigned
• Reporter: Baolong Mao
• Created: 04/May/17 08:33
• Updated: 30/Jun/17 01:43
• Resolved: 30/Jun/17 01:43

Description

public long getNonDfsUsed() throws IOException {
    long actualNonDfsUsed = getActualNonDfsUsed();
    if (actualNonDfsUsed < reserved) {
      return 0L;
    }
    return actualNonDfsUsed - reserved;
  }

The code block above is the function to caculate nonDfsUsed, but in fact it will let the result to be 0L out of expect. Such as this following situation:

du.reserved = 50G
Disk Capacity = 2048G
Disk Available = 2000G
Dfs used = 30G

usage.getUsed() = dirFile.getTotalSpace() - dirFile.getFreeSpace()
= 2048G - 2000G
= 48G
getActualNonDfsUsed = usage.getUsed() - getDfsUsed()
= 48G - 30G
= 18G
18G < 50G, so the function `getNonDfsUsed` actualNonDfsUsed < reserved, and the NonDfsUsed will return 0, is that logic make sense?