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Ankur Agarwal
Asked: 2017-09-12 20:26:11 +0800 CST

Understanding stat, du and ls -l output on my nfs mount

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ls -l f.txt
-rwxrwxr-x 1 abc abc 1161 Sep  1 02:02 f.txt

stat f.txt
  File: `f.txt'
  Size: 1161        Blocks: 34         IO Block: 524288 regular file
Device: 38h/56d Inode: 6448956669  Links: 1
Access: (0775/-rwxrwxr-x)  Uid: ( 1024/   carle)   Gid: (  100/   users)
Access: 2017-09-09 02:02:36.000000000 -0700
Modify: 2017-09-09 02:02:36.000000000 -0700
Change: 2017-09-11 20:42:00.709807459 -0700

du -h f.txt
17K wiki.txt
  1. Why is f.txt occupying 17K (17408 bytes) on disk ?
  2. What is IO Block size ? Why is it 524288 bytes long and is not equal to filesystem block size (assuming file system block size is 17K) ?

Whats going on here ?

linux

2 Answers

    1. Why is f.txt occupying 17K (17408 bytes) on disk?

    I assume you are referring to the difference of the size reported by ls -l f.txt and the blocks occupied. Normally these numbers are pretty close to each other. As Sorcha already mentioned the file occupies 34 blocks and each block reported here normally has 512 bytes. You can verify that with stat -c "%B" f.txt. If you do the math you will get 17408 bytes.
    Normally the Linux filesystems has a block size of 4096 bytes, so anything below 512 bytes would nevertheless allocate 4096 bytes or 8*512 bytes on disk, which is the smallest allocatable size in the filesystem.
    In your case it seems the blocksize of the filesystem is 17kbytes. For further clarification you would have to check the filesystem on the NFS server where the files are stored.

    1. What is IO Block size? Why is it 524288 bytes long and is not equal to filesystem block size (assuming file system block size is 17K)?

    What you see here is, taken from man stat, the optimal I/O transfer size hint and in case of NFS, this refers to the rsize/wsize mount option of NFS instead of the filesystem block size which normally is 4096 bytes. Run stat f.txt on the NFS server, which holds the filesystem on disk, to see the difference.

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  2. Why is f.txt occupying 17K (17408 bytes) on disk ? What is IO Block size ?

    Because the block size of the partition is 17408 bytes. So, yours files will be splitted in part of this size and the file which have a size smaller than 17k will occupe 1 block so 17k.

    Why is it 524288 bytes long and is not equal to filesystem block size (assuming file system block size is 17K) ?

    Because the block size of your hard drive is 512 bytes. And if you do 34x512 you will have 17408 bytes the size on your file system.

    And the IO block is the index of your block not his size

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