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

[Brassow Jonathan]

On Sep 22, 2014, at 7:35 AM, Romu wrote:

> 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?
> 

Sorry, I haven't used dm-era yet.  However, it does appear that you are perhaps specifying the wrong devices when creating the era device?  Looks like you might be allowing the era target and the cache target to use the same metadata area at the same time - causing them to corrupt each other's metadata area?

 brassow
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