[PVE-User] Ceph: Some trouble creating OSD with journal on a sotware raid device...

[Marco Gaiarin]

Mandi! Alwin Antreich
  In chel di` si favelave...

> I have to ask a more general question here, why are you putting the journal on a RAID1?

For safety?

> For better performance and less
> complexity the journal should reside on standalone SSDs. With the RAID1 you limit the speed of the journal, then it
> would be better to reside the journal on the OSD disks itself.

I know that. But i'm setting up a little ceph cluster, using as network
backend only gigabit ethernet, so my bottleneck is mostly the 50GB/s of
the network.
Also, i cannot efford to buy a SSD for every OSD, and using the same SSD
for many/all the OSD in the box is a big SPoF.

So i'm using (software) raid1, confident enought that the penalty of
the raid cannot impact so much overral.


> > The proxmox correctly see the 4 OSD candidate disks, but does not see the
> > journal partition. So i've used commandline:
> pveceph is a wrapper around ceph tools and a dependency for pveceph is smartmontools. So mdadm doesn't list smart
> attributes and this might be why it's not seeing it. But this is more a guess and should be verified by someone who
> knows better.

I suppose that.

I'm a bit unconfident with the error/warning message printed ad the
general behaviour.
AFAI've understood, ceph can use for journal disks, partition and even
files.

Probably 'md' devices are nor partition nor disks, and ceph get
confused.

Would be better, for example, to simply put journal on files? Eg,
format the md device, mount it and create inside the journal files?


Thanks.

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