Re: How to normally expand OSD’s capacity?

Ronny Aasen <ronny+ceph-users@xxxxxxxx> · Thu, 10 May 2018 17:04:22 +0200



    On 10.05.2018 12:24, Yi-Cian Pu wrote:

    
        Hi All,
         
        We are wondering if there is any way to
            expand OSD’s capacity. We are studying about this and
            conducted an experiment.
            However, in the result, the size of expanded capacity is
            counted on the USED part
            rather than the AVAIL one. The following shows the process
            of our experiment:
         
        1.      
            We
            prepare a small cluster of luminous v12.2.4 and write some
            data into pool. The
            osd.1 is manually deployed and it uses a disk partition of
            size 100GB (the
            whole disk size is 320GB).
        =====================================================================
        [root@workstation
            /]# ceph osd df
        ID CLASS
            WEIGHT  REWEIGHT SIZE USE    AVAIL 
            %USE  VAR  PGS
         0  
            hdd
            0.28999  1.00000 297G 27062M   271G 
            8.89 0.67  32
         1  
            hdd
            0.09999  1.00000 100G 27062M 76361M 26.17
            1.97  32
                           
            TOTAL 398G 54125M   345G 13.27
        MIN/MAX VAR:
            0.67/1.97  STDDEV: 9.63
        =====================================================================
         
        2.      
            Then,
            we expand the disk partition used by osd.1 by the following
            steps:
        (1)    
            Stop
            osd.1 daemon
        (2)    
              Use “parted”
            command to expand 50GB of the disk partition.
        (3)    
              Restart
            osd.1 daemon
         
        3.      
              After
            we do the above steps, we have the result that the expanded
            size is counted on
            USED part.
        =====================================================================
        [root@workstation
            /]# ceph osd df
        ID CLASS
            WEIGHT  REWEIGHT SIZE USE    AVAIL 
            %USE  VAR  PGS
         0  
            hdd
            0.28999  1.00000 297G 27063M   271G 
            8.89 0.39  32
         1  
            hdd
            0.09999  1.00000 150G 78263M 76360M 50.62
            2.21  32
                            TOTAL
            448G   102G  
            345G 22.94
        MIN/MAX VAR:
            0.39/2.21  STDDEV: 21.95
        =====================================================================
         
        This is what we have tried, and the result
            looks very confusing. We’d really want to 
        know if there is any way to normally expand
            OSD’s capacity. Any feedback or suggestions would be much
            appreciated.
         
      
    you do not do this in ceph

    
    you would most likely not partition the osd drive, you use the whole
    drive.  so you would never get into the position to need to
    increase. 

    you add space by adding osd's and adding nodes, so increasing osd
    size is not logical

    
    if you must for some oddball reason...   you can remove (drain or
    destroy)  - repartition - add the osd and let ceph backfill the
    drive. 

    or you can just make a new osd with the remaining disk space.

    since the space increase will change the crushmap there is no way to
    avoid some data movement, anyway. 

    
    mvh

    Ronny Aasen

  
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