F20 System Wide Change: SSD cache

[Conrad Meyer]

On Mon, 15 Jul 2013 13:57:39 -0400
DJ Delorie <dj at redhat.com> wrote:
> I think this is a bad idea, at least for my setup.  I
> really don't want my small expensive boot SSD being beaten
> to death trying to cache a multi-terabyte array, especially
> since I have plenty of RAM that already serves that purpose
> (the machine rarely reboots).

Actually, bcache is very good about *not* wearing out SSDs --
it writes in giant erase block-sized portions and likely you
can tune how much is written.

And either of these layers must be turned on by an admin --
it's not going to be shoved down your throat.

> At the very least, this feature should be disabled if the
> SSD is the boot/root drive.  When SSDs fail, they fail
> completely, and it's irresponsible to cause early failure
> on a drive that's critical for booting and OS operation.

By default, bcache runs a write-through cache -- it only
caches clean data. If the caching SSD dies, the bcache layer
can just forward requests to spinning drive. No data is lost.

(Bcache has a writeback mode where data loss is possible. I
do not recommend this mode.)

> Also, I think such features should be postponed
> until/unless there's a clear and obvious way to
> configure/disable them that doesn't involve installing
> additional packages or editing obscure text files.

Again -- no one is forcing you to use this. It's opt-in.

Conrad