scanning filesystem at boot?

[jfabernathy]

I was watching the console log during boot and noticed a delay of about 30 seconds related to BTRFS scanning a filesystem. Here is part of dmesg:

[    2.173969] Btrfs loaded, crc32c=crc32c-intel, zoned=yes
[    2.194162] BTRFS: device fsid e99dc575-cc5f-4d4b-b7eb-4f4837ef2855 devid 1 transid 17423 /dev/sdb scanned by btrfs (303)
[    2.195036] BTRFS: device fsid e99dc575-cc5f-4d4b-b7eb-4f4837ef2855 devid 2 transid 17423 /dev/sda scanned by btrfs (303)
[    2.195871] BTRFS: device fsid cd982c5d-ac4f-4c80-a975-9c30b40cdaa5 devid 1 transid 438 /dev/nvme0n1p3 scanned by btrfs (303)
[   33.342839] BTRFS info (device nvme0n1p3): flagging fs with big metadata feature
[   33.344032] BTRFS info (device nvme0n1p3): using free space tree
[   33.345214] BTRFS info (device nvme0n1p3): has skinny extents
[   33.350773] BTRFS info (device nvme0n1p3): enabling ssd optimizations

The interesting thing to me is the scan of sda and sdb which are a 4TB mirror with 800GB of active data took no time to scan but the nvme boot drive which is only 500GB with only ~16GB of data took around 30 seconds.

Is this just normal or do I have something wrong in my fstab?

# / was on /dev/nvme0n1p3 during installation
UUID=cd982c5d-ac4f-4c80-a975-9c30b40cdaa5 /               btrfs   defaults,subvol=@,ssd,noatime,compress=zstd,space_ cache=v2,autodefrag 0       0

# /boot/efi was on /dev/nvme0n1p1 during installation
UUID=3613-BB33  /boot/efi       vfat    umask=0077      0       1

UUID=cd982c5d-ac4f-4c80-a975-9c30b40cdaa5 /home               btrfs   defaults,subvol=@home,ssd,noatime,compress=zstd,sp ace_cache=v2,autodefrag 0       0

UUID=1da0dcaf-a1b5-46c6-8af0-fa711c22feea none            swap    sw              0       0
#
# /data mirror using /dev/sda /dev/sdb
UUID=e99dc575-cc5f-4d4b-b7eb-4f4837ef2855 /data         btrfs   defaults,noatime,compress=zstd,space_cache=v2,auto defrag 0 0

[oshunluvr]

I'm gonna say normal to exists but not 30 seconds worth. I'd reboot and see if it happens again. Maybe your filesystem was flagged as dirty or some other activity not logged was happening.

For comparison, all the btrfs mentions in my dmesg:

stuart@office:/var/log$ dmesg |grep -i btrfs
[Mon Feb  7 09:18:24 2022] Btrfs loaded, crc32c=crc32c-intel, zoned=yes
[Mon Feb  7 09:18:24 2022] BTRFS: device label storage devid 1 transid 856 /dev/sdc2 scanned by btrfs (345)
[Mon Feb  7 09:18:24 2022] BTRFS: device label root_backup devid 1 transid 61254 /dev/sdd2 scanned by btrfs (345)
[Mon Feb  7 09:18:24 2022] BTRFS: device label 970Pro devid 1 transid 3065328 /dev/nvme0n1p3 scanned by btrfs (345)
[Mon Feb  7 09:18:24 2022] BTRFS info (device nvme0n1p3): flagging fs with big metadata feature
[Mon Feb  7 09:18:24 2022] BTRFS info (device nvme0n1p3): disk space caching is enabled
[Mon Feb  7 09:18:24 2022] BTRFS info (device nvme0n1p3): has skinny extents
[Mon Feb  7 09:18:24 2022] BTRFS info (device nvme0n1p3): enabling ssd optimizations
[Mon Feb  7 09:18:25 2022] BTRFS info (device nvme0n1p3): use lzo compression, level 0
[Mon Feb  7 09:18:25 2022] BTRFS info (device nvme0n1p3): enabling auto defrag
[Mon Feb  7 09:18:25 2022] BTRFS info (device nvme0n1p3): disk space caching is enabled
[Mon Feb  7 09:18:42 2022] BTRFS info (device sdd2): flagging fs with big metadata feature
[Mon Feb  7 09:18:42 2022] BTRFS info (device sdd2): use lzo compression, level 0
[Mon Feb  7 09:18:42 2022] BTRFS info (device sdd2): enabling auto defrag
[Mon Feb  7 09:18:42 2022] BTRFS info (device sdd2): disk space caching is enabled
[Mon Feb  7 09:18:42 2022] BTRFS info (device sdd2): has skinny extents

There is a 17 second gap there, but its a GAP not a pause.

[oshunluvr]

Also for comparison, my mount options from "mount":

/dev/nvme0n1p3 on / type btrfs (rw,noatime,compress=lzo,ssd,space_cache,autodefrag,subvolid=2820,subvol=/@KDEneon)

myfstab entry:

UUID=60834933-1e99-4d5c-922c-9abbc373e172 / btrfs noatime,space_cache,compress=lzo,autodefrag,subvol=@KDEneon 0 1

The only obvious difference at this point is you have "defaults" in your options.

[jfabernathy]

Sorry, I forgot that I have a "wait-for" systemd service that keeps some things from happening until my Network Tuners are discoverable. I think this maybe the root of the delay.

I got rid of the "defaults" in fstab but that had no effect, so I then remembered the Network tuners' delay.