[Ocfs2-users] how to find out the real size of a reflink ?

[Lentes, Bernd]

----- On Jan 13, 2021, at 3:42 AM, Gang He ghe at suse.com wrote:

> Hi Lentes,
> 
> you can use "o2info --filestat yourfile" to identify how many data
> clusters for a cloned file are shared with the original file.
> Of course, the cloned file does not share meta-data blocks with the
> original file, only shares the data clusters.
> e.g.
> ghe-nd1:/rear/test # o2info --filestat dd.1.ref
>   File: dd.1.ref
>   Size: 8589934592      Blocks: 16777216   IO Block: 4096   regular file
> Device: fe00h/65024d    Inode: 355844      Links: 1
>  Frag%: 0.01            Clusters: 2097152  Extents: 157    Score: 2
> Shared: 2097152         Unwritten: 0       Holes: 0        Xattr: 0
> Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
> Access: 2021-01-13 10:08:06.561968304 +0800
> Modify: 2021-01-13 10:07:52.74642661
> Change: 2021-01-13 10:07:52.77958163
> 
> Please refer to "Shared: 2097152" item.
> 

Hi Gang,

thanks for your information.

i did it:

ha-idg-1:/mnt/ocfs2 # o2info --filestat reflink/vm_amok.raw
  File: reflink/vm_amok.raw
  Size: 880469343744    Blocks: 1719666688 IO Block: 4096   regular file
Device: fe13h/65043d    Inode: 583953      Links: 1
 Frag%: 6.60            Clusters: 839681   Extents: 55431  Score: 7
Shared: 839681          Unwritten: 0       Holes: 0        Xattr: 0
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2021-01-12 23:18:07.920405221 +0100
Modify: 2021-01-12 22:40:07.806758460 +0100
Change: 2021-01-12 22:40:08.404660948 +0100
ha-idg-1:/mnt/ocfs2 #

ha-idg-1:/mnt/ocfs2 # o2info --filestat vm_amok.raw
  File: vm_amok.raw
  Size: 880469343744    Blocks: 1719666688 IO Block: 4096   regular file
Device: fe13h/65043d    Inode: 8257821     Links: 1
 Frag%: 6.60            Clusters: 839681   Extents: 55421  Score: 7
Shared: 836667          Unwritten: 0       Holes: 0        Xattr: 0
Access: (0644/-rw-r--r--)  Uid: (  488/srvGeoClue)   Gid: (  487/     ntp)
Access: 2021-01-13 14:29:43.496432144 +0100
Modify: 2021-01-13 14:48:02.745794317 +0100
Change: 2021-01-13 14:48:02.745794317 +0100

Some questions:

What is a cluster ?
What is an extent ?
Shouldn't the number of the shared clusters be the same for both files ?
During runtime, the number of shared clusters for the reflink stays the same,
for the original file it's reducing. Is that expected behaviour ?

Bernd
Helmholtz Zentrum München

Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
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