Re: Ceph Luminous RocksDB vs WalDB?

Igor Fedotov <ifedotov@xxxxxxx> · Wed, 27 Jun 2018 13:12:50 +0300



    Hi Pardhiv,
    there is no WalDB in Ceph.
    It's WAL (Write Ahead Log) that is a way to ensure write safety
      in RocksDB. In other words - that's just a RocksDB subsystem which
      can use separate volume though.

    
    In general For BlueStore/BlueFS one can either allocate separate
      volumes for WAL and DB or have them on the same volume. The latter
      is the common option.
    The separated layout makes sense when you have tiny but
      super-fast device (for WAL) and less effective (but still fast)
      larger drive for DB. Not to mention the third one for user
      data....
    E.g. HDD (user data) + SDD (DB) + NVME  (WAL) is such a layout.
    

    So for you case IMO it's optimal to have merged WAL+DB at NVME
      and data at SSD. Hence no need for separate WAL volume.

    
    Regards,
    Igor

    
    On 6/26/2018 10:22 PM, Pardhiv Karri
      wrote:

    
      Hi,
        

        I am playing with Ceph Luminous and getting confused
          information around usage of WalDB vs RocksDB.
        

        I have 2TB NVMe drive which I want to use for Wal/Rocks DB
          and have 5 2TB SSD's for OSD. 
        I am planning to create 5 30GB partitions for RocksDB on
          NVMe drive, do I need to create partitions of WalDB also on
          NVMe drive or does RocksDB does same work as WalDB plus having
          metadata on it? 
        

        So my question is do I really need to use WalDB along with
          RocksDB or having RocksDB only is fine?
        
          
          Thanks,
          Pardhiv K
          

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