Update CHANGELOG.md and README.md about dropped virtio-blk support.

Author: alakae

CHANGELOG.md

@@ -1,6 +1,19 @@
 ## unreleased
 
 ## v3.6.0 - 2026.01.15
+
+⚠️ **Update 2026.02.04: Breaking Change**  
+We regret to inform you that this release includes a refactoring that drops support for 
+cluster nodes using `virtio-blk`. Unfortunately, this effect was missed during our review
+and only discovered post-release.
+
+If your cluster contains nodes provisioned before October 1st, 2020, or in some
+customer-specific setups before mid-2021, we recommend checking the output of
+`lsblk` to ensure that your nodes are not affected. If the output of `lsblk`
+contains volume names in the form `vdX`, you are still using `virtio-blk` and
+**should not update to this release**. In this case, we recommend to either
+provision new nodes (that will automatically use `virtio-scsi`) or pin to v3.5.6.
+
 * The minimum supported Kubernetes version is now 1.28.
 * Upgrade all sidecars to latest version
   * Please note the RBAC changes as a result of this upgrade

README.md

@@ -316,7 +316,8 @@ Please use the following options with care.
 In the `v1.3.0` release the default CSI volumes per node limit of has been increased
 to 125 (previously 23). To take advantage of the higher CSI limit you must ensure that
 all your cluster nodes are using `virtio-scsi` devices (i.e. `/dev/sdX` devices are used).
-This is the default for servers created after October 1st, 2020.
+This is the default for servers created from publicly available images after October 1st, 2020.
+Some customer-specific setups used `virtio-blk` until mid-2021.
 
 If you want to use a different value, for example because one of your nodes does not use
 `virtio-scsi`, you can set the following environment variable for the `csi-cloudscale-plugin`