I'm going to jump in here with a few points. - ceph-disk was replaced for two reasons: (1) It's design was centered around udev, and it was terrible. We have been plagued for years with bugs due to race conditions in the udev-driven activation of OSDs, mostly variations of "I rebooted and not all of my OSDs started." It's horrible to observe and horrible to debug. (2) It was based on GPT partitions, lots of people had block layer tools they wanted to use that were LVM-based, and the two didn't mix (no GPT partitions on top of LVs).
- We designed ceph-volome to be *modular* because antipicate that there are going to be lots of ways that people provision the hardware devices that we need to consider. There are already two: legacy ceph-disk devices that are still in use and have GPT partitions (handled by 'simple'), and lvm. SPDK devices where we manage NVMe devices directly from userspace are on the immediate horizon--obviously LVM won't work there since the kernel isn't involved at all. We can add any other schemes we like. - If you don't like LVM (e.g., because you find that there is a measurable overhead), let's design a new approach! I wouldn't bother unless you can actually measure an impact. But if you can demonstrate a measurable cost, let's do it. - LVM was chosen as the default appraoch for new devices are a few reasons: - It allows you to attach arbitrary metadata do each device, like which cluster uuid it belongs to, which osd uuid it belongs to, which type of device it is (primary, db, wal, journal), any secrets needed to fetch it's decryption key from a keyserver (the mon by default), and so on. - One of the goals was to enable lvm-based block layer modules beneath OSDs (dm-cache). All of the other devicemapper-based tools we are aware of work with LVM. It was a hammer that hit all nails. - The 'simple' mode is the current 'out' that avoids using LVM if it's not an option for you. We only implemented scan and activate because that was all that we saw a current need for. It should be quite easy to add the ability to create new OSDs. I would caution you, though, that simple relies on a file in /etc/ceph that has the metadata about the devices. If you lose that file you need to have some way to rebuild it or we won't know what to do with your devices. That means you should make the devices self-describing in some way... not, say, a raw device with dm-crypt layered directly on top, or some other option that makes it impossible to tell what it is. As long as you can implement 'scan' and get any other info you need (e.g., whatever is necessary to fetch decryption keys) then great. sage _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
