A little disclaimer, I have never used multipath with Ceph.
On 28.07.2021 20:19, Peter Childs wrote:
I have a number of disk trays, with 25 ssd's in them, these are
attached to
my servers via a pair of sas cables, so that multipath is used to join
the
together again and maximize speed etc.
Using cephadm how can I create the osd's?
You can use the commands in the documentation [1] "ceph orch daemon add
osd <host>:<path to multipath device>"
But you need to configure the LVM correctly to make this work.
It looks like it should be possible to use ceph-volume but I've not
really
worked out yet how to access ceph-volume within cephadm. Even if I've
got
to format them with lvm first. (The docs are slightly confusing here)
It looks like the ceph disk inventory system can't cope with multipath?
If by "ceph disk inventory system" you mean OSD service specification[2]
then yes, I don't think it's possible to use it with multipath.
When you add a disk to Ceph with cephadm it will use LVM to create a
Physical Volume(PV) of that device and create Volume Group(VG) on the
disk and then create a Logical Volume(LV) that use the whole VG.
And the configuration in Ceph reference the VG/LV so Ceph should not
have a problem with multipath.
But since you have multipath, LVM might have a problem with that if not
configured correctly.
LVM will scan disk for LVM signature and try to create the devices for
the LV it finds.
So you need to make sure that the LVM only scan the multipath device
paths and not the individual disk the OS sees.
[1] https://docs.ceph.com/en/latest/cephadm/osd/#creating-new-osds
[2]
https://docs.ceph.com/en/latest/cephadm/osd/#advanced-osd-service-specifications
--
Kai Stian Olstad
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