Re: RHEL6.6 dm-cache and dm-era

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On 2014/9/16 4:25, Brassow Jonathan wrote:
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

Thanks, I have successfully set up LVM caching with dm-cache, works like a charm. However, I still haven't any useful documentation about how to set dm-era. Any idea?

Thanks
Romu

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