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@@ -989,6 +989,22 @@ Then you do the backup and look at the log output:
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You can use the ``stat`` command on files to manually look at fs metadata to debug if
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there is any unexpected change triggering the ``M`` status.
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+When borg runs inside a virtual machine, there are some more things to look at:
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+
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+Some hypervisors (e.g. kvm on proxmox) give some broadly compatible CPU type to the
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+VM (usually to ease migration between VM hosts of potentially different hardware CPUs).
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+
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+It is broadly compatible because they leave away modern CPU features that could be
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+not present in older or other CPUs, e.g. hardware acceleration for AES crypto, for
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+sha2 hashes, for (P)CLMUL(QDQ) computations useful for crc32.
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+
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+So, basically you pay for compatibility with bad performance. If you prefer better
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+performance, you should try to expose the host CPU's misc. hw acceleration features
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+to the VM which runs borg.
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+
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+On Linux, check ``/proc/cpuinfo`` for the CPU flags inside the VM.
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+For kvm check the docs about "Host model" and "Host passthrough".
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+
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See also the next few FAQ entries for more details.
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.. _a_status_oddity:
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Thomas Waldmann