Re: Help with Bluestore WAL

David Turner <drakonstein@xxxxxxxxx> · Thu, 22 Feb 2018 01:39:51 +0000

There WAL sis a required party of the osd. If you remove that, then the osd is missing a crucial part of itself and it will be unable to start until the WAL is back online. If the SSD were to fail, then all osds using it would need to be removed and recreated on the cluster.

On Tue, Feb 20, 2018, 9:44 PM Konstantin Shalygin <k0ste@xxxxxxxx> wrote:

        Hi,
    We were recently testing luminous with bluestore. We have 6 node cluster with 12 HDD and 1 SSD each, we used ceph-volume with LVM to create all the OSD and attached with SSD WAL (LVM ). We create individual 10GBx12 LVM on single SDD for each WAL. So all the OSD WAL is on the singe SSD. Problem is if we pull the SSD out, it brings down all the 12 OSD on that node. Is that expected behavior or we are missing any configuration ?

Yes, you should plan your failure domain, i.e. what will be
      happens with your cluster if one backend ssd suddenly dies.
    Also you should plan mass failures of your ssd/nvme, so rule of
      thumb - don't overload your flash backend with osd. Recommend is
      ~4 osd per ssd/nvme.

    k

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