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

[Romu]

I tried the following command to set up my era target but the command
immediately panics the system and the system reboots.

# dmsetup create MyEra --table "0 41941903 era
/dev/mapper/VG-CacheDataLV_cmeta /dev/mapper/VG-OriginLV 4096"

The metadata dev and the origin dev are all part of a LVM cache LV.
VG-CacheDataLV_cmeta is the cache metadata LV on the smaller and faster
device, VG-OriginLV is the origin LV on the faster and slower device,
41941903 is the total sector number of the device of OriginLV (the LV takes
100% space of the device), 4096 is the block size of OriginLV, I have run
'mkfs.ext4 /dev/mapper/VG-OriginLV' before running the dmsetup command.

Below is the message in /var/log/messages after running the dmsetup
comnmand:

kernel: device-mapper: era: sb_check failed: magic 1623043: wanted
2126579579
kernel: device-mapper: block manager: superblock validator check failed for
block 0
kernel: device-mapper: era: couldn't read_lock superblock


Any idea?

Thanks
Romu

2014-09-18 16:27 GMT+08:00 Romu Hu <huruomu at gmail.com>:

> 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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/dm-devel/attachments/20140922/264d7ef0/attachment.htm>