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perf(quickemu): improve disk I/O defaults (cache,aio) #1837

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flexiondotorg merged 1 commit into from
Jan 25, 2026
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perf(quickemu): improve disk I/O defaults (cache,aio) #1837

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5 changes: 3 additions & 2 deletions quickemu
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Original file line number Diff line number Diff line change
Expand Up @@ -1887,8 +1887,9 @@ function vm_boot() {

# Add the disks
# - https://turlucode.com/qemu-disk-io-performance-comparison-native-or-threads-windows-10-version/
# Optimise disk I/O: enable TRIM/discard and zero detection for thin provisioning
DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap"
# Optimise disk I/O: enable TRIM/discard, zero detection for thin provisioning,
# writeback caching and threaded async I/O
DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap,cache=writeback,aio=threads"
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@cubic-dev-ai cubic-dev-ai bot Jan 25, 2026

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P2: Setting cache=writeback as a default for all VM disks increases the risk of data loss on host failures (docs warn that writeback reports writes complete before they hit storage). Consider leaving cache unspecified or using a safer mode by default and making writeback opt‑in.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At quickemu, line 1892:

<comment>Setting `cache=writeback` as a default for all VM disks increases the risk of data loss on host failures (docs warn that writeback reports writes complete before they hit storage). Consider leaving cache unspecified or using a safer mode by default and making writeback opt‑in.</comment>

<file context>
@@ -1887,8 +1887,9 @@ function vm_boot() {
-    DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap"
+    # Optimise disk I/O: enable TRIM/discard, zero detection for thin provisioning,
+    # writeback caching and threaded async I/O
+    DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap,cache=writeback,aio=threads"
 
     if [[ "${boot}" == *"efi"* ]]; then
</file context>
Suggested change
DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap,cache=writeback,aio=threads"
DRIVE_OPTIMISATIONS="discard=unmap,detect-zeroes=unmap,aio=threads"


if [[ "${boot}" == *"efi"* ]]; then
QCOW2CODE=$(is_firmware_qcow2 "${EFI_CODE}")
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