[linux-lvm] Cache block size warning

Zdenek Kabelac zdenek.kabelac at gmail.com
Thu Nov 19 08:56:41 UTC 2015

Dne 19.11.2015 v 08:27 Ciprian Hacman napsal(a):
> Hi,
> We are configuring lvm with SSD caching on some of our boxes in AWS. When the
> cache is initialised, we see this in logs:
>     device-mapper*: cache: You have created a cache device with a lot of
>     individual cache blocks (4915200)*
>     *               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.*
> Is this something to worry? If so, how can we improve it?

If you have lots of kernel memory - it's probably ok.
Otherwise you may try to use bigger chunk size.

e.g.  --chunksize 512K   or even more:

lvcreate --type cache-pool -L300G vg/cpool

lvcreate -H --chunksize 512K -L1.5T   --name data  vg/cpool

It's possible future version of lvm2 will try to create this by default.


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