Lenovo Tab 2 Partition Layout
Why are Boot and Recovery one partition?

This you can find answered in a Wiki entry at Github. Quoting the relevant part:


  Since MTK devices use the uboot mechanism, partitions including boot and recovery, are not revealed as separate partitions, but rather accessed sequencially by size and start parameters.


You can see that reflected in your output of /proc/dumchar_info: size is the second column, start sector the third. Think of it like "disk images stored on a raw medium" (not an exact description, but easier to visualize).

Which one is the system partition?

My first guess (by the name) was sec_ro (as system is "ro", read only). But that's not exact enough. To find out, you'd need the sector size and the size of your /system partition, then you can do the maths: /proc/emmc gives you the "number of sectors" each partition occupies, in HEX. sec_ro accordingly occupies 0x3000 sectors, that would be 12288 in decimal. At a sector size of 512 bytes1 that would be 6 MB – too small :) A better guess probably is p5 named "android", which sums up to 1.5 GB – that seems to be the correct size. cache is /cache and usrdata will be the /data partition.



1: according to Understanding MTK’s MBR/EBR File Format