[dm-devel] RHEL6.6 dm-cache and dm-era

[Brassow Jonathan]

On Sep 14, 2014, at 9:24 PM, Romu Hu wrote:

> Hi,
> 
> According to https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6-Beta/html-single/6.6_Release_Notes/index.html#bh-storage, dm-cache and dm-era have been added into RHEL6.6 as technology preview, but I couldn't find any other documentation about using dm-cache and dm-era.  I found the following utilities in
> 
> /usr/sbin/era_check
> /usr/sbin/era_dump
> /usr/sbin/era_invalidate
> 
> /usr/sbin/cache_check
> /usr/sbin/cache_dump
> /usr/sbin/cache_repair
> /usr/sbin/cache_restore
> 
> I guess these utilities are related to dm-era and dm-cache, respectively.  There are only manpages for the cache utilities. After reading the manpages I still have no clue how to use these technologies.  I want to do a sanity check of these technologies on my SAN storage.  Is it possible to try dm-cache and dm-era without a SSD?  e.g. using ram to imitate a fast block device..
> 
> Any idea?

You can use cache to teir any block device over another.  Layering faster, smaller drives over slower, larger ones is the point; but for testing non-performance things you can still do it.  For the cache target, it would be a more inclusive test to go through LVM.  The lvmcache.7 man page would help out with that.  There is no dm-era support in LVM ATM.

 brassow