[linux-lvm] lvmcache performance

John Stoffel john at stoffel.org
Mon Feb 8 16:51:07 UTC 2016

>>>>> "Joe" == Joe Thornber <thornber at redhat.com> writes:

Joe> 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?

Joe> Firstly, if you have the latest software, I suggest you switch to
Joe> the smq cache policy which is generally out performing the old mq
Joe> policy substantially.

Is there a tool to help measure lvmcache performance metrics and
display how well the cache is working?

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

I'm personally using it for caching VMs and NFS data dirs.  Seems to
be working well... but I wonder.  

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