Re: Ceph Luminous RocksDB vs WalDB?

Igor Fedotov <ifedotov@xxxxxxx> · Thu, 28 Jun 2018 23:58:05 +0300



    I think the second variant is what you need. But I'm not the guru
      in ceph-deploy so there might be some nuances there...
    Anyway the general idea is to have just a single NVME partition
      (for both WAL and DB) per OSD.

    
    Thanks,
    Igor

    
    On 6/27/2018 11:28 PM, Pardhiv Karri
      wrote:

    
      Thank you Igor for the response.
        

        So do I need to use this,
        

        ceph-deploy osd create --debug --bluestore --data /dev/sdb
          --block-wal /dev/nvme0n1p1 --block-db /dev/nvme0n1p2
          cephdatahost1

        
        or 
        

        ceph-deploy osd create --debug --bluestore --data /dev/sdb
          --block-db /dev/nvme0n1p2 cephdatahost1

        
        where /dev/sdb is ssd disk for osd
        /dev/nvmen0n1p1 is 10G partition
        /dev/nvme0n1p2 is 25G partition
        

        Thanks,
        Pardhiv K
      
      
        On Wed, Jun 27, 2018 at 9:08 AM Igor Fedotov <ifedotov@xxxxxxx>
          wrote:

        
            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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      -- 

      
        Pardhiv
                      Karri

                "Rise and Rise again until LAMBS
                  become LIONS" 
        

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