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

[Loic Tortay]

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      |