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Comment by throw0101a | Hacker News Reader

> Not to take away from the merits of ZFS, but this sounds like something that 2 disks with software RAID1 would prevent from happening.

You're not wrong. And if there's a mechanical issue with a drive and it dies / stops spinning, then you'll probably get an alert and can swap it.

But if there's any kind of bit rot or data corruption, and it only happens on one side of the (traditional) RAID1 mirror, how will you (a) know that it actually occurred, or (b) know which side is good bits and which side has bad bits?

With ZFS and checksums, you can be confident that your data is still healthy. Depending on the data, this may be an important consideration.

zfs send-recv is also very handy for doing incremental backups.

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What ZFS does here is not enough for me. I need to be alerted to changes done also above the file system layer, like by malware or accidental deletion etc. Only way I have found to solve that is to have checksum tool above the file system. If something is wrong, I restore from backup, so zfs does not give me anything...

I don't personally do this, but if you're taking scheduled snapshots of your ZFS filesystems, you could also have a scheduled job (say, nightly) that emails you a "zfs diff" [0] between the current snapshot and the one from 24 hours ago. It won't tell you that you've been hit by malware, but an unexpected spike in changes could be something worth investigating.

[0] - https://docs.oracle.com/cd/E36784_01/html/E36835/gkkqz.html

You can do a zfs diff command on two snapshots or a snapshot and current dataset as zfs takes a just-in-time snapshot of the live dataset.

> I need to be alerted to changes done also above the file system layer [...]

As others have mentioned, would "zfs diff ..." be useful?

* https://www.thegeekdiary.com/how-to-identify-zfs-snapshot-di...

As the name suggests, "snapshots" are read-only and so cannot be altered. You could either copy/rsync the modified file/s to the live location, or do a rollback to a particular snapshot:

* https://www.thegeekdiary.com/solaris-zfs-how-to-create-renam...

If the machine is compromised in some way, you could reinstall and do a "zfs send-recv" of a pool from a remote system.

You can clone the snapshot (so its clone become writable, not the snapshot itself!) and you even can promote a snapshot to a "parent" filesystem (reverse parent-child).

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