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Captured disk activity from last 2 days using below command but unable to find out why it is writing so much (426MB) on root partition

iotop -oPa -d 2


Total DISK READ :       0.00 B/s | Total DISK WRITE :       0.00 B/s
Actual DISK READ:       0.00 B/s | Actual DISK WRITE:       0.00 B/s
  PID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                                                                                   
  239 be/3 root          0.00 B    426.21 M  0.00 %  0.17 % [jbd2/sdd2-8]
 2678 be/4 root        961.21 M    107.91 M  0.00 %  0.03 % <emby mono-sgen>
 2198 be/4 root          0.00 B      0.00 B  0.00 %  0.02 % udisksd --no-debug
 6402 be/4 root         16.00 K      0.00 B  0.00 %  0.07 % [kworker/u4:1]
13162 be/4 root         16.00 K      0.00 B  0.00 %  0.09 % [kworker/u4:2]

I have below disk

/dev/sdd2 on / type ext4 (rw,noatime,errors=remount-ro)
/dev/sda1 on /media/<user>/2TB_EXT4 type ext4 (rw,nosuid,nodev,noatime,uhelper=udisks2)
/dev/sdb1 on /media/<user>/2TB_EXT4_2 type ext4 (rw,nosuid,nodev,noatime,uhelper=udisks2)
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jdb2 is the process that updates the journal for ext4 systems. It seems that this is updated even though the filesystem is mounted "noatime".

There are ways of running a completely read-only root file system, see https://wiki.debian.org/ReadonlyRoot and https://help.ubuntu.com/community/aufsRootFileSystemOnUsbFlash, for example.

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