From: Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com>
To: pve-devel@lists.proxmox.com
Cc: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
Subject: [pve-devel] [PATCH pve-storage] qcow2 format: enable subcluster allocation by default
Date: Wed, 3 Jul 2024 16:24:47 +0200 [thread overview]
Message-ID: <mailman.249.1720016708.331.pve-devel@lists.proxmox.com> (raw)
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From: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
To: pve-devel@lists.proxmox.com
Subject: [PATCH pve-storage] qcow2 format: enable subcluster allocation by default
Date: Wed, 3 Jul 2024 16:24:47 +0200
Message-ID: <20240703142447.602210-1-alexandre.derumier@groupe-cyllene.com>
extended_l2 is an optimisation to reduce write amplification.
Currently,without it, when a vm write 4k, a full 64k cluster
need to be writen.
When enabled, the cluster is splitted in 32 subclusters.
We use a 128k cluster by default, to have 32 * 4k subclusters
https://blogs.igalia.com/berto/2020/12/03/subcluster-allocation-for-qcow2-images/
https://static.sched.com/hosted_files/kvmforum2020/d9/qcow2-subcluster-allocation.pdf
some stats for 4k randwrite benchmark
Cluster size Without subclusters With subclusters
16 KB 5859 IOPS 8063 IOPS
32 KB 5674 IOPS 11107 IOPS
64 KB 2527 IOPS 12731 IOPS
128 KB 1576 IOPS 11808 IOPS
256 KB 976 IOPS 9195 IOPS
512 KB 510 IOPS 7079 IOPS
1 MB 448 IOPS 3306 IOPS
2 MB 262 IOPS 2269 IOPS
Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
---
src/PVE/Storage/Plugin.pm | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/PVE/Storage/Plugin.pm b/src/PVE/Storage/Plugin.pm
index 6444390..31b20fe 100644
--- a/src/PVE/Storage/Plugin.pm
+++ b/src/PVE/Storage/Plugin.pm
@@ -561,7 +561,7 @@ sub preallocation_cmd_option {
die "preallocation mode '$prealloc' not supported by format '$fmt'\n"
if !$QCOW2_PREALLOCATION->{$prealloc};
- return "preallocation=$prealloc";
+ return "preallocation=$prealloc,extended_l2=on,cluster_size=128k";
} elsif ($fmt eq 'raw') {
$prealloc = $prealloc // 'off';
$prealloc = 'off' if $prealloc eq 'metadata';
--
2.39.2
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next reply other threads:[~2024-07-03 14:24 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-07-03 14:24 Alexandre Derumier via pve-devel [this message]
2024-09-11 11:44 ` Fiona Ebner
2024-11-14 8:31 ` DERUMIER, Alexandre via pve-devel
[not found] ` <98cdc246d14fdfc5dcfedf09dd4bc596acb0814f.camel@groupe-cyllene.com>
2024-11-25 15:06 ` Fiona Ebner
2024-11-26 1:38 ` DERUMIER, Alexandre via pve-devel
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