Op 29 september 2016 om 16:09 schreef Emmanuel Florac [off-list ref]:


Le Wed, 28 Sep 2016 21:14:50 +0200 (CEST)
Wido den Hollander [off-list ref] écrivait:

quoted

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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