[linux-lvm] lvmcache performance

Nikolaus Rath Nikolaus at rath.org
Mon Feb 8 22:05:24 UTC 2016

On Feb 08 2016, Joe Thornber <thornber at redhat.com> wrote:
> On Sun, Feb 07, 2016 at 10:43:30AM -0800, Nikolaus Rath wrote:
>> Is that the wrong expectation? But even then, shouldn't I at least see
>> some improvement?
> Firstly, if you have the latest software, I suggest you switch to the
> smq cache policy which is generally out performing the old mq policy
> substantially.

Will try, thanks.

> Secondly, I think you may need to reset your expectations a bit.
> dm-cache is a slow moving cache.  It monitors IO, detectings hotspots
> on the disk and then 'promotes' those regions to the SSD.  You may
> find that the reads that occur during a boot, occur only infrequently
> once the system is booted.

Well, yes, but since in my case the cache is bigger than the origin,
shouldn't eventually *everything* end-up in the cache?

Is there a way to tell how often I need to access a block for it to be
promoted? I was hoping that the {read,write}_promote_adjustement
settings would actually cause promotion on the first access.


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