On Thu, Oct 25, 2018 at 5:38 AM jiaruo bai <baijiaruo@xxxxxxxxx> wrote: > > Hi all, > > I want to use bcache(ssd as cache and sas/sata as backend disk) to > improve performance in ceph v12.2.x, and bluestore uses lvm as the > default. > When the bcache backend disk breakdown, I want to remove bcache > device, so I remove the lvm on it firstly, but the OS is panic during > removing. You might want to try out dmcache which we have used with no apparent problems (certainly no OS panics) > > my questions are: > 1. I want to know if it is necessary to use lvm? I got some > considerations from > http://lists.ceph.com/pipermail/ceph-users-ceph.com/2018-February/024388.html, > but are there more? It is the current default when provisioning a new OSD, so all the Ceph tooling is using it. It isn't necessary as you can try and find a different way to provide devices for the OSD, like partitions. That would require manual provisioning, while ceph-volume could help with the systemd handling (see `ceph-volume simple scan` command) > 2. If I do not use lvm, what harms are there in the future? for > example the upgrade of ceph. Hard to say what changes we might introduce that could cause issues for a custom OSD provisioning scheme, but I don't think there is any at the moment
