Filesystem data changes while mounting

[p7cq]

I have a filesystem that has new data written to it during the mounting process. I noticed this happening on each reboot, then managed to narrow it down to the mounting process.

Doing

zfs get mountpoint pool/volume1 -Hovalue
none

zfs list -t snapshot -Housed pool/volume1@snapshot1
0

zfs set mountpoint=/mnt/volume1 pool/volume1; zfs list -t snapshot -Housed pool/volume1@snapshot1
8192

shows the filesystem has new data, when in fact it has not (that is, data created/modified by a user or a by a user created process). - In contrast

zfs get mountpoint pool/volume2 -Hovalue
none

zfs list -t snapshot -Housed pool/volume2@snapshot2
0

zfs set mountpoint=/mnt/volume2 pool/volume2; zfs list -t snapshot -Housed pool/volume2@snapshot2
0

I tried zstream dump, but is not telling me much and it seems there's no (easy?) way to see what is actually transmitted in the stream.

Any ideas on what could be altering the data in the filesystem during mount?

[IvanVolosyuk]

• In some desktop environments there are programs which scan newly mounted drives.
• There can be 'atime' changes just on read, readdir accesses. You can change it with zfs set atime=off dataset

[p7cq]

This is on my workstation, indeed, with uptimes spanning days at most. It always starts in run level 3, as I don't always need the Window Manager. This particular filesystem is not shared (NFS, Samba etc) nor touched by anything/anyone other than me explicitly adding data to it. I even ran the commands from a script after a reboot, with lsof continuously running in the background. Nothing touches pool/volume1. The other filesystem, pool/volume2 is part of the same "lifecycle" as pool/volume1- it does not have this issue.

The pool has atime=off and relatime=on, inherited by all datasets. The commands were run while inside /root (on a different pool), not /mnt/volume1.