SPANISH VERSION: https://groups.google.com/forum/m/#!topic/vegnuli/Lr-corc2Xrw (with updates)
The Journaling file system will always touch the dataWhen mounting (and unmounting) several journaling file systems with only "-o ro" mount flag a different number of data writes will happened, thats happened due journaling, so this its a list of options that must be use when preform the mount command and u must passed with "-o" flag:
|File system||When data writes happen||Notes|
|Ext3/Etx4||File system requires journal recovery||To disable recovery: use "noload" flag, or use "ro,loop" flags, or use "ext2" file system type|
|btfs||File system has unfinished transactions||"nolog" flag does not work (see man mount). To disable journal updates: use "ro,loop" flags|
|ReiserFS||File system has unfinished transactions||"nolog" flag does not work (see man mount). To disable journal updates: use "ro,loop" flags|
|XFS||Always (when unmounting)||"norecovery" flag does not help (fixed in recent 2.6 kernels). To disable data writes: use "ro,loop" flags.|
Read process can be interpreted as write processIf u perform read operations over mounted or inclusivelly non-mounted filesystem, the operative system wil try to make reading again, for sure its not a itsefl problem, then a hardware problem, that's, the second must be avoid, ah of course stupid winbuntu linux always perform that checks, and also of course systemd now.
During boot process the init modified script will test existing partions for Ext3/4 file systems on fixed media, and this happened due these scripts mount every supported file system type on every supported media type using only "-o ro" flag in order to find a root file system image, as we didit, with the previous topic, those are not enought.