Re: [pve-devel] [PATCH qemu-server] qcow2: increase cache-size to 1GB

["DERUMIER, Alexandre via pve-devel" <pve-devel@lists.proxmox.com>]

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From: "DERUMIER, Alexandre" <alexandre.derumier@groupe-cyllene.com>
To: "pve-devel@lists.proxmox.com" <pve-devel@lists.proxmox.com>, "f.ebner@proxmox.com" <f.ebner@proxmox.com>, "f.gruenbichler@proxmox.com" <f.gruenbichler@proxmox.com>
Subject: Re: [pve-devel] [PATCH qemu-server] qcow2: increase cache-size to 1GB
Date: Fri, 3 Oct 2025 14:05:23 +0000
Message-ID: <7fc8439e1fb61c341e637daae60362ecf0a36f79.camel@groupe-cyllene.com>

> > 

>>But the max value might even be reached for relatively small disks.
>>And
>>there are users that have a lot of VMs with rather small disks. For
>>them, the increase in memory consumption would be quite big I
>>suppose!

Currently the qemu default cache size is 32MB , enough to handle 256 GB
images. 

so, I'm not sure It'll make so much difference. even if user have a lot
of 512GB images (100images for example), 50TB, it'll add an extra
100x32MB = 3GB memory .

sure, if user have 100 imagesx8TB, 800TB stockage on 1 host, It'll
increase memory to around 100x1GB = 100Gb memory. ^_




>>Yes, I'd also be in favor of using something calculated from the
>>size.
>>We could additionally add a drive configuration option to override
>>the
>>value if we really want to.


and if we use something calculated from the size of the disk, it'll not
help to limit global memory usage. 








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