[Gluster-users] Block size reported from FUSE-client

[Maik Kulbe]

> So st_blocks on FUSE mount is different from st_blocks on backend for the
> same file?

Yes. Just a quick example: I create a file with 5 Bytes in size. I theory Gluster should report 8 x 512 Byte blocks, because the underlying XFS uses a 4K block size. Instead, it reports the minimum count of blocks the file size would fit in:

client> echo test > /gluster/tmp/test.txt

client> stat /gluster/tmp/test.txt
  File: `/gluster/tmp/test.txt'
  Size: 5         	Blocks: 1          IO Block: 131072 regular file
Device: 14h/20d	Inode: 12072747239032953097  Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-11-26 12:09:22.960828776 +0100
Modify: 2013-11-26 12:09:22.964828962 +0100
Change: 2013-11-26 12:09:22.964828962 +0100
 Birth: -

gluster> stat /bricks/0/tmp/test.txt
  File: `/bricks/0/tmp/test.txt'
  Size: 5         	Blocks: 8          IO Block: 4096   regular file
Device: ca03h/51715d	Inode: 859069733   Links: 2
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-11-26 12:09:22.957683891 +0100
Modify: 2013-11-26 12:09:22.961684089 +0100
Change: 2013-11-26 12:09:22.961684089 +0100
 Birth: -

>
> On Nov 25, 2013 8:50 AM, "Maik Kulbe" <info at linux-web-development.de>
> wrote:
>
> From man (2) stat:
>
> blksize_t st_blksize; /* blocksize for file system I/O */
> blkcnt_t  st_blocks;  /* number of 512B blocks allocated */
>
> The 128K  you are seeing is "st_blksize" which is the recommended I/O
> transfer size. The number of consumed blocks is always reported as 512
> byte blocks. The actual block size with which storage allocation
> happens
> depends on the backend filesystem.
>
> This is what was confusing me. On the file systems one of our
> programmers tested the latter one it was always showing the blocks
> allocated. So if you had a 1k file and 4k block size it would report 8
> 512-byte blocks, gluster just reports 2 blocks.
>
> Avati
>
> On Mon, Nov 25, 2013 at 7:18 AM, Maik Kulbe
> <info at linux-web-development.de> wrote:
>
> Hi,
>
> I've come to notice that the file system block size reported from stat
> on a client is 128k, which is pretty high for the small files I use.
> On
> the other hand, I tested copying smaller files to the volume and it
> seems those 128k are not the real block size - when I copy two 64k
> files
> to the volume `df` reports only a change after both files have been
> copied.
>
> So my question would be what is the real block size for the Gluster
> volume? The block size of the underlying xfs? Or something else? And
> is
> it possible to read the real block size? We wanted to use the block
> size
> reported by stat to calculate the real file size use on disk but it
> seems that is not possible with Gluster..
>
> Thank you in advance,
> Maik
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