Hi,
On 09/10/17 16:09, Sage Weil wrote:
To put this in context, the goal here is to kill ceph-disk in mimic.
One proposal is to make it so new OSDs can *only* be deployed with LVM,
and old OSDs with the ceph-disk GPT partitions would be started via
ceph-volume support that can only start (but not deploy new) OSDs in that
style.
Is the LVM-only-ness concerning to anyone?
Looking further forward, NVMe OSDs will probably be handled a bit
differently, as they'll eventually be using SPDK and kernel-bypass (hence,
no LVM). For the time being, though, they would use LVM.
This seems the best point to jump in on this thread. We have a ceph
(Jewel / Ubuntu 16.04) cluster with around 3k OSDs, deployed with
ceph-ansible. They are plain-disk OSDs with journal on NVME partitions.
I don't think this is an unusual configuration :)
I think to get rid of ceph-disk, we would want at least some of the
following:
* solid scripting for "move slowly through cluster migrating OSDs from
disk to lvm" - 1 OSD at a time isn't going to produce unacceptable
rebalance load, but it is going to take a long time, so such scripting
would have to cope with being stopped and restarted and suchlike (and be
able to use the correct journal partitions)
* ceph-ansible support for "some lvm, some plain disk" arrangements -
presuming a "create new OSDs as lvm" approach when adding new OSDs or
replacing failed disks
* support for plain disk (regardless of what provides it) that remains
solid for some time yet
On Fri, 6 Oct 2017, Alfredo Deza wrote:
Bluestore support should be the next step for `ceph-volume lvm`, and
while that is planned we are thinking of ways to improve the current
caveats (like OSDs not coming up) for clusters that have deployed OSDs
with ceph-disk.
These issues seem mostly to be down to timeouts being too short and the
single global lock for activating OSDs.
IMO we can't require any kind of data migration in order to upgrade, which
means we either have to (1) keep ceph-disk around indefinitely, or (2)
teach ceph-volume to start existing GPT-style OSDs. Given all of the
flakiness around udev, I'm partial to #2. The big question for me is
whether #2 alone is sufficient, or whether ceph-volume should also know
how to provision new OSDs using partitions and no LVM. Hopefully not?
I think this depends on how well tools such as ceph-ansible can cope
with mixed OSD types (my feeling at the moment is "not terribly well",
but I may be being unfair).
Regards,
Matthew
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