Re: XFS & LVM: unexpected cp when issuing mv

[Asdo <asdo@shiftmail.org>]

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Please paste the output of the following 2 commands:

df  /disks/sharestore/upload/

df  /disks/sharestore/download/


Michael Monnerie wrote:
> I have an unexpected behaviour and I hope someone can explain me the 
> reasons:
>
> This is an openSUSE 11.2 virtual machine within XENserver. XENserver can 
> only create 2TB disks, but I needed more. So I create 2x 2TB disks for 
> that VM. These disks have no partitions, but are straight LVM:
> # pvscan
>   PV /dev/xvdb   VG sharestore   lvm2 [1,95 TB / 0    free]
>   PV /dev/xvdc   VG sharestore   lvm2 [1,95 TB / 0    free]
>   Total: 2 [3,91 TB] / in use: 2 [3,91 TB] / in no VG: 0 [0   ]
>
> I created one VG, and then one LV:
> # vgscan
>   Reading all physical volumes.  This may take a while...
>   Found volume group "sharestore" using metadata type lvm2
> # lvscan
>   ACTIVE            '/dev/sharestore/public' [3,91 TB] inherit
>
> On that LV, I created an XFS filesystem, mounted from /etc/fstab:
> /dev/sharestore/public /disks/sharestore  xfs        
> noatime,nodiratime,logbufs=8,logbsize=256k,attr2,nobarrier,largeio,swalloc,inode64,prjquota
>
> Now when I move from one dir to another, example
> mv /disks/sharestore/upload/* /disks/sharestore/download/
>
> within some dirs it's a simple mv where only metadata is moved, but with 
> some dirs it's a physical cp+rm of the files. You can easily see that by 
> the speed of the mv, plus with iostat:
> Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-
> sz avgqu-sz   await  svctm  %util
> xvdb              0,00     0,00    0,00  647,31     0,00 28424,75    
> 87,82    18,46   29,71   0,24  15,65
> xvdc              0,00     0,40  631,14    2,40 26928,54    76,65    
> 85,25     5,56    8,69   1,56  98,84
>
> Until now I believed that a mv within one filesystem is always just a 
> metadata mv. But it seems I found a case now where even within the same 
> filesystem a physical cp+rm is done. Can someone explain me
>
> 1) why this happens
> 2) how I can prevent this?
>
> We have files >5G there, often 20G or more, so a mv should just be a 
> metadata mv, everything else is inacceptable.
> Could it be the way I created the VG + LV, that there's a cp instead mv?
> How could I create all that to get a normal behaviour?
>
> Maybe like this?:
> 1) create VG only on one disk
> 2) create LV on that disk
> 3) create XFS
> 4) extend VG to 2nd disk
> 5) extend LV to 2nd disk
> 6) xfs_growfs to 2nd disk
>
> mfg zmi
>   
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>
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