[jira] [Updated] (HDDS-5380) Get more accurate space info for DedicatedDiskSpaceUsage

["Mark Gui (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDDS-5380?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mark Gui updated HDDS-5380:
---------------------------
    Description: 
Java has 2 apis to get available space info for a mounted fs: `getFreeSpace()` and `getUsableSpace()`,  the latter is more accurate(see its java doc).

Let's do a experiment:
{code:java}
// java

import java.io.File;

public class FsSpace {
  public static void main(String args[]) {
    File file = new File(args[0]);
    System.out.println("FreeSpace: " + file.getFreeSpace());
    System.out.println("UsableSpace: " + file.getUsableSpace());
  }
}{code}
 compile it and run against my root /, let's compare with linux command 'df'.
{code:java}
// linux command line
$ java FsSpace /
FreeSpace: 49653022720           <-- A
UsableSpace: 45126942720         <-- B

$ df / -B1
Filesystem        1B-blocks        Used   Available Use% Mounted on
overlay        105553784832 55900872704 45126832128  56% /
                                             ^
                                             |
                                             C{code}
So the B and C is more close to each other, while A is larger.

Here we have about a 4GB diff on a 100GB disk for the 2 java apis.

I think that `getFreeSpace()` must only account for all unallocated space but does not take the space reserved for system use into consideration while `getUsableSpace()` do.

So we should be more conservative to prevent over consumed disk space.

P.S.

HDFS has a implemtation that use the 2 apis for different purposes, see:

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/DF.java

> Get more accurate space info for DedicatedDiskSpaceUsage
> --------------------------------------------------------
>
>                 Key: HDDS-5380
>                 URL: https://issues.apache.org/jira/browse/HDDS-5380
>             Project: Apache Ozone
>          Issue Type: Sub-task
>            Reporter: Mark Gui
>            Assignee: Mark Gui
>            Priority: Minor
>
> Java has 2 apis to get available space info for a mounted fs: `getFreeSpace()` and `getUsableSpace()`,  the latter is more accurate(see its java doc).
> Let's do a experiment:
> {code:java}
> // java
> import java.io.File;
> public class FsSpace {
>   public static void main(String args[]) {
>     File file = new File(args[0]);
>     System.out.println("FreeSpace: " + file.getFreeSpace());
>     System.out.println("UsableSpace: " + file.getUsableSpace());
>   }
> }{code}
>  compile it and run against my root /, let's compare with linux command 'df'.
> {code:java}
> // linux command line
> $ java FsSpace /
> FreeSpace: 49653022720           <-- A
> UsableSpace: 45126942720         <-- B
> $ df / -B1
> Filesystem        1B-blocks        Used   Available Use% Mounted on
> overlay        105553784832 55900872704 45126832128  56% /
>                                              ^
>                                              |
>                                              C{code}
> So the B and C is more close to each other, while A is larger.
> Here we have about a 4GB diff on a 100GB disk for the 2 java apis.
> I think that `getFreeSpace()` must only account for all unallocated space but does not take the space reserved for system use into consideration while `getUsableSpace()` do.
> So we should be more conservative to prevent over consumed disk space.
> P.S.
> HDFS has a implemtation that use the 2 apis for different purposes, see:
> hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/DF.java



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