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ZFS Feature Flags in FreeNAS

Ericloewe

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#1
Ericloewe submitted a new resource:

ZFS Feature Flags in FreeNAS - Overview of ZFS Feature Flags and their support in FreeNAS

OpenZFS' distributed development led to the introduction of Feature Flags. Instead of incrementing version numbers, support for OpenZFS features is indicated by Feature Flags.

Feature Flag states

Feature flags exist in one of three states:

disabled
The Feature Flag is not used by the pool. The pool can be imported on systems that do not support this feature flag.

enabled
The feature has been enabled for use in this pool, but no changes are in effect....
Read more about this resource...
 

danb35

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#2
Device removal allows for vdevs to be removed from a pool, subject to limitations.
This is coming in 11.2? Wow. I knew it was on the way, but didn't realize it was that close. Bit of a bummer that you lose the ability to use that pool with an older version though.
 

Ericloewe

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#3
This is coming in 11.2? Wow. I knew it was on the way, but didn't realize it was that close. Bit of a bummer that you lose the ability to use that pool with an older version though.
Yes, AFAIK it only works for single-disk vdevs for now. So mirrors need to be demoted first and RAIDZ is out of luck.

It's been in production at Delphix for a while now. Apparently they had a bunch of machines where they went "oops, we gave them a bunch of space that they'll never use, we should remove them to save some cash", which is an unusual scenario, to say the least.
 

Stux

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#4
This is coming in 11.2? Wow. I knew it was on the way, but didn't realize it was that close. Bit of a bummer that you lose the ability to use that pool with an older version though.
It’s still something you want to avoid though, as you end up with permanent block redirects in your pool.

Idea I guess is for the “oh whoops” case that shouldn’t matter, since the vdev wouldn’t have seen much usage before it’s removal

@Ericloewe thanks for putting this resource together
 

Ericloewe

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#5
It’s still something you want to avoid though, as you end up with permanent block redirects in your pool.
That's what obsolete_counts is for. It removes obsolete entries so that you're not attached to the table forever.
 

Stux

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#6
It's been in production at Delphix for a while now. Apparently they had a bunch of machines where they went "oops, we gave them a bunch of space that they'll never use, we should remove them to save some cash", which is an unusual scenario, to say the least.
Illustrates nicely the driving force behind ZFS feature development ;)
 

Ericloewe

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#7
It's kind of an ironic outcome. Oracle wanted to suppress ZFS outside its grasp, but they ended up creating the perfect environment for ZFS development to spread. A special method of version tracking needed to be created to accommodate the spread-out development.
 

Ericloewe

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#8

Ericloewe

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#9
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