ext4 performance tweaking: how to confirm data=writeback is in effect?

chconnor · 03-17-2021, 09:57 PM

Hi -- I'm experimenting with various ext4 settings on an SSD (SATA).

/etc/fstab has:

Code:

UUID=1234 / ext4 noatime,data=writeback,barrier=0,nobh,commit=60,errors=remount-ro 0       1

...but that makes the system not boot (an error relating to remounting with different journal mode) unless I also do:

Code:

# tune2fs -o journal_data_writeback /dev/sda2

...now the system boots, but I don't see "data=writeback" here:

Code:

$ findmnt /dev/sda2
TARGET SOURCE    FSTYPE OPTIONS
/      /dev/sda2 ext4   rw,noatime,nobarrier,errors=remount-ro,commit=60

How can I tell if data=writeback has taken effect?

Thanks!

chconnor · 03-17-2021, 09:59 PM

Ah, perhaps I have answered my question: journalctl -xb shows

Code:

EXT4-fs (sda2): mounted filesystem with writeback data mode. Opts: (null)
...
EXT4-fs (sda2): re-mounted. Opts: data=writeback,barrier=0,nobh,commit=60,errors=remount-ro

...but out of curiosity, is there a way to check this via CLI? Why wouldn't it show up in findmnt?