Re: Partitions on bcache devices

[Wido den Hollander <wido@42on.com>]

> Op 29 september 2016 om 16:09 schreef Emmanuel Florac <eflorac@intellique.com>:
> 
> 
> Le Wed, 28 Sep 2016 21:14:50 +0200 (CEST)
> Wido den Hollander <wido@42on.com> écrivait:
> 
> > In both cases Ceph wants to create partitions on all disks it uses.
> > By adding bcache in between the performance can be boosted really
> > well. Fast NVM-e SSDs with some large SATA drives vastly improve
> > performance.
> > 
> > Yes, you could use LVM in between, but that just adds more layers and
> > is rather complex to accomplish with the current tooling. If bcache
> > would support partitions it would all be a lot easier.
> > 
> > And next to Ceph there might be other tools which can benefit from
> > partitions on bcache, who knows?
> 
> 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 :)
> 

Thanks for the information :) Currently not really a option with Ceph.

> Second: are you absolutely sure you can't partition a bcache device?
> Does parted refuse to open and partition it? In which case, you may
> only be missing some appropriate udev rules.
> 

Yes, I'm sure. You can create the partitions, but they will not show up as devices which you can use due to a limitation in the bcache kernel driver.

Patches [0] are out there to make this work, but they are not in bcache yet.

Hence my thread if this support can be added.

Wido

[0]: https://yaple.net/2016/03/31/bcache-partitions-and-dkms/

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