▁failure ▁or ▁un rec over able ▁crash ▁should ▁occur ▁before ▁the ▁other ▁blocks ▁get ▁written , ▁the ▁system ▁will ▁have ▁to ▁be ▁reboot ed . ▁Upon ▁reboot , ▁the ▁file ▁system ▁will ▁re play ▁the ▁log ▁as ▁normal , ▁and ▁re play ▁the ▁" w inners " ▁( trans actions ▁with ▁a ▁commit ▁block , ▁including ▁the ▁invalid ▁transaction ▁above , ▁which ▁happened ▁to ▁be ▁tag ged ▁with ▁a ▁valid ▁commit ▁block ). ▁The ▁un fin ished ▁disk ▁write ▁above ▁will ▁thus ▁proceed , ▁but ▁using ▁cor rupt ▁journal ▁data . ▁The ▁file ▁system ▁will ▁thus ▁mistaken ly ▁overwrite ▁normal ▁data ▁with ▁cor rupt ▁data ▁while ▁re play ing ▁the ▁journal . ▁If ▁check sum s ▁had ▁been ▁used , ▁where ▁the ▁blocks ▁of ▁the ▁" f ake ▁winner " ▁transaction ▁were ▁tag ged ▁with ▁a ▁mut ual ▁check sum , ▁the ▁file ▁system ▁could ▁have ▁known ▁better ▁and ▁not ▁re play ed ▁the ▁cor rupt ▁data ▁onto ▁the ▁disk . ▁Journal ▁check sum ming ▁has ▁been ▁added ▁to ▁ext 4 . ▁ ▁Files ystem s ▁going ▁through ▁the ▁device ▁ma pper ▁interface ▁( including ▁software ▁RA ID ▁and ▁L VM ▁implementations ) ▁may ▁not ▁support ▁bar riers , ▁and ▁will ▁issue ▁a ▁warning ▁if ▁that ▁mount ▁option ▁is ▁used . ▁There ▁are ▁also ▁some ▁dis ks ▁that ▁do ▁not ▁properly ▁implement ▁the ▁write ▁cache ▁fl ushing ▁extension ▁necessary ▁for ▁bar riers ▁to ▁work , ▁which ▁causes ▁a ▁similar ▁warning . ▁In ▁these ▁situations , ▁where ▁bar riers ▁are ▁not ▁supported ▁or ▁practical