[PATCH pve-docs 3/3] partially fix #1989: qm: document qcow2 cache size config

[Erik Fastermann <e.fastermann@proxmox.com>]

Add a new subsection to document the new qcow2 cache config options.

Signed-off-by: Erik Fastermann <e.fastermann@proxmox.com>
---
 qm.adoc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/qm.adoc b/qm.adoc
index e6b7918..2f1e7d4 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -341,6 +341,16 @@ underlying storage. Another benefit is reduced latency (hangs) in the guest for
 very I/O-intensive host workloads, since neither the main thread nor a vCPU
 thread can be blocked by disk I/O.
 
+[[qm_hard_disk_qcow2_cache]]
+Cache Size (qcow2)
+^^^^^^^^^^^^^^^^^^
+Fine-tuning the qcow2 L2/refcount cache behavior can provide significant
+performance gains. See the
+https://gitlab.com/qemu-project/qemu/-/blob/master/docs/qcow2-cache.txt[QEMU documentation] 
+for a detailed explanation of these options. You can either configure the cache
+size directly or let Proxmox VE automatically choose a cache size based on the
+disk image size. All other options can be managed with the API.
+
 [[qm_cpu]]
 CPU
 ~~~
-- 
2.47.3