F20 System Wide Change: SSD cache

[Conrad Meyer]

On Mon, 15 Jul 2013 22:34:15 +0200
Rave it <chat-to-me at raveit.de> wrote:

> 
> Hmm,
> for me me this is more a question how can i configure
> bcache or dm-cache in a system which use more than one SSD
> and some conventional hard-disk. Seems like only you or
> some kernel devs know about how to do this. Can you give a
> configuration example for f19? For example, i use 4 SSD at
> a hardware-raid for my several systems
> (f17/f18/f19/rawhide), i called it A, i need this for
> testing compiz on baremetal for all current fedora
> releases. On a second hardware-raid- controller i have 4
> conventional disks to store my data, i called it B. So, if
> i add another SSD for bcache or dm-cache, i called C, how
> can i configure it? 1. this configuration should not
> control disk A 2. disk C should use as cache for disk B
> 
> Is this possible to configure?
> Do you have a link with more info's and configuration
> examples.
> 
> best regards,
> Wolfgang

First off -- bcache requires an additional superblock on the
backing disk / block device -- in this case, B. So you would
have to reformat the entire B array if you wanted to use
bcache on it.

With that in mind, see:
http://evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt?h=bcache-dev#n38

"""
make-bcache -B /dev/path/to/B -C /dev/new/SSD

...

The devices show up as:

  /dev/bcache<N>

As well as (with udev):

  /dev/bcache/by-uuid/<uuid>
  /dev/bcache/by-label/<label>

To get started:

  mkfs.ext4 /dev/bcache0
  mount /dev/bcache0 /mnt
"""

That document should help answer some of your questions about
bcache.

Best regards,
Conrad