Hi Emmanuel,

Zitat von Emmanuel Florac [off-list ref]:

[...]
Two points: first I'm pretty sure LVM is the preferred method nowadays
to create volumes on disks that are not boot drives. In fact, all
enterprises distros propose to set up even the boot drive with LVM
instead of partitionning and have been doing so for 10 years.
So I'm pretty sure having in ceph the option to use LVM instead of
partitionning would be a darn good thing :)

I disagree. As a matter of fact, it'd be a bad idea IMO: Unlike with  
what you have given as good examples for LVM usage, the disk layout on  
OSDs is fixed. So you're throwing in a (rather fast, but unnecessary)  
code path intended to provide flexibility, where you need none. This  
causes delays and provides potential problems that can be avoided.  
Another counter-example: You wouldn't put LVM on a disk that's  
intended as a (100%) MD-RAID volume, and add an LV as RAID member...  
you'll add a partition table for a reason, but no extra layer between  
the partition and the RAID stuff.

Second: are you absolutely sure you can't partition a bcache device?

While I haven't tried in a while, that's the way it was when I tested  
last. No partitioning of the bcache device. If you want multiple  
bcached partitions on a backing store, partition first and then create  
multiple bcached devices. This could be done with the BlueStore  
installer as well, but somebody will have to provide the code to  
optionally bcache the partitions.

Regards,
J