<html> <head> <meta http-equiv="content-type" content="text/html; charset=utf-8"> </head> <body bgcolor="#FFFFFF" text="#000000"> Dear dm-devel community, I'm trying to get familiar with dm-era but I'm stuck. What I'm trying to achieve is to have a dm-era device which keeps track of changed blocks on a seperate hard drive or logical volume/mapping in order to create a live backup solution. The documentation on dm-era is very sparse. So far I found a Gentoo wiki entry, a blog entry by Rackcorp and the official kernel doc. I tried to come up with a basic setup using a virtual machine running Ubuntu 16.04. So far I was able to create a setup that looks like this: <a href="http://i.imgur.com/LNCPima.png">http://i.imgur.com/LNCPima.png</a> To set this up, I came up with the following script: <a href="http://pastebin.com/Y3B2m7wL">http://pastebin.com/Y3B2m7wL</a> It is inspired by the setup done by Rackcorp [1]. The resulting 'lsblk' looks like this: <pre>sdb 8:16 0 256M 0 disk </pre> <pre>`-metadev-era 252:2 0 276K 0 dm </pre> <pre> |-era 252:4 0 276K 0 dm </pre> <pre> `-era-access 252:5 0 276K 0 dm </pre> <pre>sdc 8:32 0 256M 0 disk </pre> <pre>`-metadev-data 252:3 0 256M 0 dm </pre> <pre> |-era 252:4 0 276K 0 dm </pre> <pre> `-metadev-data-access 252:6 0 256M 0 dm /media/sdc-data</pre> In comparison to Rackcorp's setup, I did the following adjustment: <ul> <li>i) mounting /dev/mapper/metadev-data (or the underlying sdc) or ii) using it as an origin device for era, seemed to be mutually exclusive</li> <li>that's why I created an additional linear mapping called 'metadev-data-access' inspired by the 'era-access' device to be able to mount and write to the sdc device again</li> </ul> Basically this setup is supposed to track changed blocks on /dev/sdc and uses a mounted /dev/mapper/metadev-data-access at /media/sdc-data to access /dev/sdc on top of the dm setup. However, when reading the era metadata via 'era_dump /dev/mapper/era-access', I only get this result: <pre><superblock uuid="" block_size="4096" nr_blocks="1" current_era="1"></pre> <pre> <era_array></pre> <pre> <era block="0" era="0"/></pre> <pre> </era_array></pre> <pre></superblock></pre> Why is there only one block listed? Shouldn't that list exactly as much blocks as my 'metadev-data' device has, since it is the origin for the era target? Or is there some basic misunderstanding in my interpretation of how dm-era is supposed to work and be used? Please be so kind and shed some light on this! [1] <a href="http://blog.rackcorp.com/2016/03/dm-era-device-for-backups/">http://blog.rackcorp.com/2016/03/dm-era-device-for-backups/</a> Best Regards, Markus Hentsch Cloud&Heat Technologies </body> </html>