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@xxxxxxxxx>:
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?On 2014/9/16 4:25, Brassow Jonathan wrote:
On Sep 14, 2014, at 9:24 PM, Romu Hu wrote:
Hi,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.
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?
brassow
Thanks
Romu
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