[Libguestfs] [PATCH v2v] input: Disable multi-conn in VDDK input mode

The cow filter unconditionally enables multi-conn (because it is safe). However this causes an unintended consequence with the VDDK plugin. Multiple VDDK handles are opened (one per multi-conn connection), and for some reason, possibly internal locking, they conflict with each other. This manifests itself as API calls taking between 2 and 7 times longer to serve (especially QueryAllocatedBlocks which seems to slow down most). Avoid this by adding nbdkit-multi-conn-filter with multi-conn-mode=disable on top which disables multi-conn advertisement. Virt-v2v -ic esx://... -it vddk -o null, before this change: [ 2.8] Opening the source [ 11.4] Inspecting the source [ 16.2] Checking for sufficient free disk space in the guest [ 16.2] Converting Windows 10 Enterprise to run on KVM virt-v2v: This guest has virtio drivers installed. [ 25.5] Mapping filesystem data to avoid copying unused and blank areas [ 67.3] Closing the overlay [ 68.0] Assigning disks to buses [ 68.0] Checking if the guest needs BIOS or UEFI to boot [ 68.0] Copying disk 1/1 █ 100% [****************************************] [ 416.4] Creating output metadata [ 416.4] Finishing off After this change: [ 2.8] Opening the source [ 12.6] Inspecting the source [ 18.7] Checking for sufficient free disk space in the guest [ 18.7] Converting Windows 10 Enterprise to run on KVM virt-v2v: This guest has virtio drivers installed. [ 36.1] Mapping filesystem data to avoid copying unused and blank areas [ 77.0] Closing the overlay [ 77.9] Assigning disks to buses [ 77.9] Checking if the guest needs BIOS or UEFI to boot [ 77.9] Copying disk 1/1 █ 100% [****************************************] [ 332.3] Creating output metadata [ 332.3] Finishing off --- input/nbdkit_vddk.ml | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/input/nbdkit_vddk.ml b/input/nbdkit_vddk.ml index 79ec363bce..c2c3cceb93 100644 --- a/input/nbdkit_vddk.ml +++ b/input/nbdkit_vddk.ml @@ -157,10 +157,30 @@ See also the virt-v2v-input-vmware(1) manual.") libNN let cmd = Nbdkit.add_filter_if_available cmd "cacheextents" in (* IMPORTANT! Add the COW filter. It must be furthest away - * except for the rate filter. + * except for the multi-conn and rate filters. *) let cmd = Nbdkit.add_filter cmd "cow" in + (* The cow filter unconditionally enables multi-conn (because it is + * safe). However this causes an unintended consequence with the VDDK + * plugin. Multiple VDDK handles are opened (one per multi-conn + * connection), and for some reason, possibly internal locking, they + * conflict with each other. This manifests itself as API calls taking + * between 2 and 7 times longer to serve (especially QueryAllocatedBlocks + * which seems to slow down most). + * + * Avoid this by adding nbdkit-multi-conn-filter with + * multi-conn-mode=disable on top which disables multi-conn + * advertisement. + *) + let cmd = + if Nbdkit.probe_filter "multi-conn" then ( + let cmd = Nbdkit.add_filter cmd "multi-conn" in + let cmd = Nbdkit.add_arg cmd "multi-conn-mode" "disable" in + cmd + ) + else cmd in + (* If the filter supports it, enable cow-block-size (added in * nbdkit 1.27.6). This helps to reduce fragmentated small * extent and read requests. -- 2.32.0