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Fix discard alignment issue in VM due to QCOW2 bitmap layer - #3922
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Signed-off-by: Stéphane Graber <stgraber@stgraber.org>
…rity qcow2 drops discards that don't cover a whole cluster, so the guest must be told the cluster size to align its requests. Signed-off-by: Stéphane Graber <stgraber@stgraber.org>
bensmrs
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Aug 29, 2026
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Our use of a QCOW2 layer for bitmap tracking causes QEMU to use 64k aligned chunks for discard. We weren't communicating that to the guest leading to misaligned requests that QEMU would then just drop.
In the worst case this was causing IncusOS to fallback to a full zeroing of the entire 50GiB+ drive rather than a single discard request.