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

[Anand Avati]

You are seeing a side-effect of http://review.gluster.com/3631. Which
means: if your backend filesystem uses 4KB blocks, then the value reported
by gluster will be at worst 7 blocks smaller (4KB / 512 - 1).


On Tue, Nov 26, 2013 at 3:13 AM, Maik Kulbe
<info at linux-web-development.de>wrote:

> 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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>> Gluster-users at gluster.org
>> http://supercolony.gluster.org/mailman/listinfo/gluster-users
>>
>
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