Checksum defaults to SHA512 for NON-dedup datasets
Description
Problem/Justification
Impact
Activity
William Gryzbowski November 3, 2021 at 6:31 PM
This will be reverted for U6.1
Ievgen Stepanovych October 28, 2021 at 7:46 AM
Seems like this change requires more work. We are reverting the checksum option completely for u6.1
Winnie Linnie October 25, 2021 at 9:46 PM(edited)
@Bonnie Follweiler I don't believe this ticket requires a debug file?
It's a bug introduced with an update of TrueNAS Core, from version 12.0-U5.1 ---> 12.0-U6 in which it was not correctly implemented (as described above.) It's not unique to my system.
Here is the ticket where it was introduced: https://jira.ixsystems.com/browse/NAS-110523
The ticket was for an Improvement to default the Checksum to SHA512 when selecting (or inheriting) ZFS Deduplication upon creating a new dataset. If the user intentionally enables Dedup, then it works as expected: a dialog popup informs the user that the default Checksum has been changed to SHA512 (and it in fact does change Checksum to SHA512 if it was not already chosen.)
However, it seems that this "fix" applied to 12.0-U6 accidentally made SHA512 the default Checksum for all new datasets, regardless of Dedup or not.
On top of that, the dialog popup is incorrect, and must be re-worded to reflect a more accurate warning.
It reads:
"Default Checksum Warning"
"The default 'Checksum' value for ZFS pools used to be SHA256. Our testing has shown that SHA512 performs better.
So, we have changed the default value from SHA256 to SHA512. You can change it back in 'Advanced Options'."
This is incorrect / ambiguous / misleading for multiple reasons:
1) Checksum is applied on a per-dataset level, not the entire pool.
2) The default checksum for Dedup datasets was SHA256. The default for non-Dedup datasets always was (and still should be) On (i.e, Fletcher4). The popup is ambiguous and does not clarify this very important detail (of Dedup vs non-Dedup).
3) The popup only appears when the user enables ZFS Deduplication, yet it makes no mention of Dedup vs non-Dedup in the warning. (As I explain in point #2 above.)
Bonnie Follweiler October 25, 2021 at 3:07 PM
Thank you for the report, @Winnie Linnie .
Can you please attach a debug file to this ticket? To generate a debug file on TrueNAS CORE, log in to the TrueNAS web interface, go to System > Advanced, then click Save Debug and wait for the file to download to your local system.
Winnie Linnie October 25, 2021 at 2:11 AM
This has performance implications, since Fletcher4 (the default "On" when dedup is disabled) is faster than SHA512, like for like.
TrueNAS Core 12.0-U6 introduced a new Checksum default when creating new datasets with ZFS Deduplication enabled. However, it appears this new feature was not correctly implemented, as it defaults to SHA512 even when dedup is not selected.
In fact, it just outright defaults to SHA512 without any user intervention; in which dedup is disabled by default.
If dedup is not selected, the default Checksum should remain as On . It should only switch to default SHA512 if dedup is selected .
Forum post for reference:
https://www.truenas.com/community/threads/new-checksum-default-when-did-this-happen.96142/post-664809