[linux-lvm] Quick question regarding lvm-cache

[linux-lvm] Quick question regarding lvm-cache

[Devin Vance]

Greetings,

Short version:

Is there anyway to adjust the cache blocksize of the lvm cache with the 
lvm tools?

Long version:

I have been exploring the new lvm-cache features within rhel7 (tech 
preview, I know), and with a cache of 1.4TiB in size I noticed these 
warnings within the logs.

device-mapper: cache: You have created a cache device with a lot of 
individual cache blocks (1638400) All these mappings can consume a lot 
of kernel memory, and take some time to read/write.Please consider 
increasing the cache block size to reduce the overall cache block count.

However, I cannot find any straightforward method with which to adjust 
this cache block size. I did find this documentation which explains how 
to do so with device mapper: 
https://www.kernel.org/doc/Documentation/device-mapper/cache.txt Is 
there anyway to do this with the lvm tools, or is this yet to be developed?


Many thanks,
Devin

Re: [linux-lvm] Quick question regarding lvm-cache

[Mike Snitzer]

On Sat, Nov 21 2015 at  6:10pm -0500,
Devin Vance <devin@linbit.com> wrote:

> Greetings,
> 
> Short version:
> 
> Is there anyway to adjust the cache blocksize of the lvm cache with
> the lvm tools?

Kind of amazing that the lvmcache man page doesn't touch on
this... there is an opportunity there ;)

Anyway, lvcreate's -c argument (aka chunksize) is re-used to specify a
different cache blocksize.