[gpfsug-discuss] du --apparent-size and quota

[Kumaran Rajaram]

Hi,

>> If I'm not mistaken even with SS5 created filesystems, 1 MiB FS block size implies 32 kiB sub blocks (32 sub-blocks).

Just to add: The /srcfilesys seemed to have been created with GPFS version 4.x which supports only 32 sub-blocks per block.

-T                 /srcfilesys              Default mount point
-V                 16.00 (4.2.2.0)          Current file system version
                   14.10 (4.1.0.4)          Original file system version
--create-time      Tue Feb  3 11:46:10 2015 File system creation time
-B                 1048576                  Block size
-f                 32768                    Minimum fragment (subblock) size in bytes
--subblocks-per-full-block 32               Number of subblocks per full block


The /dstfilesys was created with GPFS version 5.x which support greater than 32 subblocks per block. /dstfilesys does have 512 subblocks-per-full-block with 8KiB subblock size since file-system blocksize is 4MiB. 


-T                 /dstfilesys              Default mount point
-V                 23.00 (5.0.5.0)          File system version
--create-time      Tue May 11 16:51:27 2021 File system creation time
-B                 4194304                  Block size
-f                 8192                     Minimum fragment (subblock) size in bytes
--subblocks-per-full-block 512              Number of subblocks per full block

Hope this helps,
-Kums



-----Original Message-----
From: gpfsug-discuss-bounces at spectrumscale.org <gpfsug-discuss-bounces at spectrumscale.org> On Behalf Of Loic Tortay
Sent: Tuesday, June 1, 2021 10:57 AM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>; Ulrich Sibiller <u.sibiller at science-computing.de>; gpfsug-discuss at gpfsug.org
Subject: Re: [gpfsug-discuss] du --apparent-size and quota

On 6/1/21 4:26 PM, Ulrich Sibiller wrote:
[...]
> )
> 
> While trying to understand what's going on here I found this on the 
> source file system (which is valid for all files, with different 
> number of course):
> 
> $ du --block-size 1 /srcfilesys/fileset/filename
> 65536   /srcfilesys/fileset/filename
> 
> $ du --apparent-size --block-size 1 /srcfilesys/fileset/filename
> 3994    /srcfilesys/fileset/filename
> 
> $ stat /srcfilesys/fileset/filename
>   File: ‘/srcfilesys/fileset/filename’
>   Size: 3994            Blocks: 128        IO Block: 1048576 regular 
> file
> Device: 2ah/42d Inode: 23266095    Links: 1
> Access: (0660/-rw-rw----)  Uid: (73018/ cpunnoo)   Gid: (50070/  
> dc-rti)
> Context: system_u:object_r:unlabeled_t:s0
> Access: 2021-05-12 20:10:13.814459305 +0200
> Modify: 2020-07-16 11:08:41.631006000 +0200
> Change: 2020-07-16 11:08:41.630896177 +0200
>  Birth: -
> 
Hello,
This looks like the sub-block overhead.
If I'm not mistaken even with SS5 created filesystems, 1 MiB FS block size implies 32 kiB sub blocks (32 sub-blocks).
The sub-block is the minimum disk allocation for files (if the file content is too large to be kept in the inode, when that is supported on the specific GPFS filesystem).

The "Blocks" value displayed by "stat" is in 512 bytes unit, so 128*512 = 65536 (which is consistent with "du"): two 32 kiB sub-blocks due to data replication.

The "--apparent-size" option to "du" uses the user visible size not the actual disk usage (per the man page), so 3994 is also consistent w/ "stat" output.

AFAIK, GPFS space quotas count the sub-blocks not the apparent sizes, so again this would be consistent with the overhead.

Beside the overhead, hard-links in the source FS (which, if I'm not mistaken, are not handled by "rsync" unless you specify "-H") and in some cases spare files can also explain the differences.


Loïc.
-- 
|       Loïc Tortay <tortay at cc.in2p3.fr> - IN2P3 Computing Centre      |
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