Make ganging redundancy respect redundant_metadata property #17073
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amotin
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Feb 20, 2025
amotin
approved these changes
Feb 21, 2025
added 12 commits
February 21, 2025 09:30
ZFS gang block headers are currently fixed at 512 bytes. This is increasingly wasteful in the era of larger disk sector sizes. This PR allows any size allocation to work as a gang header. It also contains supporting changes to ZDB to make gang headers easier to work with. Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
Signed-off-by: Paul Dagnelie <[email protected]>
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This PR is based on top of #17004, and includes those changes. Only the last commit contains new changes. The PR is marked as ready for review, but should not be merged until #17004 is finalized.
Motivation and Context
The redundant_metadata setting in ZFS allows users to trade resilience for performance and space savings. This applies to all data and metadata blocks in zfs, with one exception: gang blocks. Gang blocks currently just take the
copiesproperty of the IO being ganged and, if it's 1, sets it to 2. This means that we always make at least two copies of a gang header, which is good for resilience. However, if the users care more about performance than resilience, their gang blocks will be even more of a penalty than usual.Description
We add logic to calculate the number of gang headers copies directly, and store it as a separate IO property. This is stored in the IO properties and not calculated when we decide to gang because by that point we may not have easy access to the relevant information about what kind of block is being stored. We also check the redundant_metadata property when doing so, and use that to decide whether to store an extra copy of the gang headers, compared to the underlying blocks.
There is also a new test to verify that gang headers are stored redundantly in roughly the way that we want, plus some changes to the other gang block tests to make the new test (and other tests) easier to work with.
How Has This Been Tested?
Mostly the new zfs-test suite test, plus similar manual testing.
Types of changes
Checklist:
Signed-off-by.