From: Thomas Lamprecht <t.lamprecht@proxmox.com>
To: Elias Huhsovitz <e.huhsovitz@proxmox.com>,
Markus Frank <m.frank@proxmox.com>,
pve-devel@lists.proxmox.com
Subject: Re: [PATCH qemu-server v1] {pbs-,vma-}restore: disable caching for LVM-thin
Date: Mon, 9 Nov 2026 17:12:40 +0100 [thread overview]
Message-ID: <72e56f92-b00b-4835-874d-c8fce2298619@proxmox.com> (raw)
In-Reply-To: <DLMMW8NCI0RY.1QDRTI5M2G25Z@proxmox.com>
Am 23.09.26 um 12:46 schrieb Elias Huhsovitz:
> Thanks for spotting this potential optimization.
> Gave this quick try and results seem to be mixed.
>
> When restoring from a pbs I saw a time reduction of ~35%.
> When restoring locally from a .vma.zst file i saw a time increase of
> ~81%.
Might be due to us triggering 64 KiB writes on VMA, which can get
coalesced if caching is active thus papering over the non-ideal IO
behavior from us there. Without cache the storage sees each such
request explicitly, causing more IO operations. This should be
improved with [0] which coalesces the requests directly in VMA, thus
reducing amount of syscalls (not really relevant on such IO heavy
workloads) due to submitting up to a full extent of 58 x 64 KiB
clusters – so 3.6 MiB – in one go.
[0]: https://lore.proxmox.com/pve-devel/20261109160210.3380582-1-t.lamprecht@proxmox.com/
prev parent reply other threads:[~2026-11-09 16:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-08 12:37 [PATCH qemu-server v1] {pbs-,vma-}restore: disable caching for LVM-thin Markus Frank
2026-09-23 10:46 ` Elias Huhsovitz
2026-11-09 16:12 ` Thomas Lamprecht [this message]
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