cache_mode none

cache_mode none

[Kingsly John]

Hi!

I've been trying out bcache over the last couple of weeks and couldn't find
this explained anywhere.

On my setup here while writing with cache_mode set to none, there's a
near constant 30-40kb/sec write happening to the flash device all through.
But in the other modes the amount of data written is significantly
higher.(While copying the same set of files into a freshly formatted bcache
device)

Does setting cache_mode to none just disable the cache for reading or does it
disable it for both reading and writing?

If it's only disabled for reads, then with cache_mode set to none would
bcache still recover from an unclean shutdown?

Kingsly


-- 

Re: cache_mode none

[Kent Overstreet]

On Thu, Oct 04, 2012 at 03:54:06PM +0530, Kingsly John wrote:
> Hi!
> 
> I've been trying out bcache over the last couple of weeks and couldn't find
> this explained anywhere.
> 
> On my setup here while writing with cache_mode set to none, there's a
> near constant 30-40kb/sec write happening to the flash device all through.
> But in the other modes the amount of data written is significantly
> higher.(While copying the same set of files into a freshly formatted bcache
> device)
> 
> Does setting cache_mode to none just disable the cache for reading or does it
> disable it for both reading and writing?
> 
> If it's only disabled for reads, then with cache_mode set to none would
> bcache still recover from an unclean shutdown?

In cache_mode none, nothing new will be added to the cache (neither from
writes nor cache misses), but the cache is still kept consistent -
that's the reason for the writing that still happens to the flash
devices, it's invalidating the cache whenever you do a write.

It will still read from the cache, because there might still be dirty
data in the cache.