I just checked an OSD and the "block" entry is indeed linked to storage
using a /dev/mapper uuid LV, not a /dev/device. When ceph builds an
LV-based OSD, it creates a VG whose name is "ceph-uuuuu", where "uuuu"
is a UUID, and an LV named "osd-block-vvvv", where "vvvv" is also a
uuid. So although you'd map the osd to something like /dev/vdb in a VM,
the actual name ceph uses is uuid-based (and lvm-based) and thus not
subject to change with alterations in the hardware as the uuids are part
of the metadata in VGs and LVs created by ceph.
Since I got that from a VM, I can't vouch for all cases, but I thought
it especially interesting that a ceph was creating LVM counterparts even
for devices that were not themselves LVM-based.
And yeah, I understand that it's the amount of OSD replicate data that
counts more than the number of hosts, but when an entire host goes down
and there are few hosts, that can take a large bite out of the replicas.
Tim
On 4/11/25 10:36, Anthony D'Atri wrote:
I thought those links were to the by-uuid paths for that reason?
On Apr 11, 2025, at 6:39 AM, Janne Johansson <icepic...@gmail.com> wrote:
Den fre 11 apr. 2025 kl 09:59 skrev Anthony D'Atri <anthony.da...@gmail.com>:
Filestore IIRC used partitions, with cute hex GPT types for various states and
roles. Udev activation was sometimes problematic, and LVM tags are more
flexible and reliable than the prior approach. There no doubt is more to it
but that’s what I recall.
Filestore used to have softlinks towards the journal device (if used)
which pointed to sdX where that X of course would jump around if you
changed the number of drives on the box, or the kernel disk detection
order changed, breaking the OSD.
--
May the most significant bit of your life be positive.
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