63 lines
3.1 KiB
Diff
63 lines
3.1 KiB
Diff
From 6346bcf6e574b46defaf24baac185c32bc41ba30 Mon Sep 17 00:00:00 2001
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Message-ID: <6346bcf6e574b46defaf24baac185c32bc41ba30.1729611062.git.jdenemar@redhat.com>
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From: Peter Krempa <pkrempa@redhat.com>
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Date: Thu, 10 Oct 2024 08:42:20 +0200
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Subject: [PATCH] docs: Add warning about using a cleared image with
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VIR_MIGRATE_PARAM_MIGRATE_DISKS_DETECT_ZEROES_ZEROES
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The migration parameter causes zero detection to be enabled and zero
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blocks are *not* transferred to the destination. This means that users
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must provide pre-cleared images that read all zero, otherwise the
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non-zero blocks on destination which reside in places where the source
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has zero blocks would be kept intact corrupting the image.
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As not transferring and overwriting the zero blocks is what the feature
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is supposed to do the users need to provide the proper environment.
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Document the requirement, both in API and in the virsh man page for the
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'--migrate-disks-detect-zeroes' option.
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Signed-off-by: Peter Krempa <pkrempa@redhat.com>
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Reviewed-by: Jiri Denemark <jdenemar@redhat.com>
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(cherry picked from commit 332ee4931a84ec23e7f6fcb963083318c1307dc7)
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https://issues.redhat.com/browse/RHEL-61177
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---
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docs/manpages/virsh.rst | 4 +++-
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include/libvirt/libvirt-domain.h | 5 ++++-
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2 files changed, 7 insertions(+), 2 deletions(-)
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diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
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index 87de338644..bb1b2e5cc4 100644
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--- a/docs/manpages/virsh.rst
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+++ b/docs/manpages/virsh.rst
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@@ -3425,7 +3425,9 @@ transfer via the comma separated ``disk-list`` argument.
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The *--migrate-disks-detect-zeroes* option which takes a comma separated list of
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disk target names enables zeroed block detection for the listed migrated disks.
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These blocks are not transferred or allocated on destination, effectively
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-sparsifying the disk at the cost of CPU overhead.
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+sparsifying the disk at the cost of CPU overhead. Users must ensure that any
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+pre-created storage source is cleared and thus reads all-zeroes before using
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+this option as otherwise the destination image may become corrupted.
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With *--copy-storage-synchronous-writes* flag used the disk data migration will
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synchronously handle guest disk writes to both the original source and the
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destination to ensure that the disk migration converges at the price of possibly
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diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
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index a6afacbc22..c83dc299e7 100644
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--- a/include/libvirt/libvirt-domain.h
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+++ b/include/libvirt/libvirt-domain.h
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@@ -1245,7 +1245,10 @@ typedef enum {
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*
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* virDomainMigrate* params multiple field: The multiple values that list
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* the block devices for which zero detection (to avoid transferring zero blocks)
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- * is to be enabled. This may increase CPU overhead of the migration. At the
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+ * is to be enabled. Users must ensure that any pre-created storage source on
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+ * the destination will be cleared and thus read all-zeroes before using this
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+ * feature, otherwise the destination image may become corrupted.
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+ * This may increase CPU overhead of the migration. At the
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* moment this is only supported by the QEMU driver but not for the tunnelled
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* migration.
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*
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--
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2.47.0
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