OSDOCS-14322# Add hyperdisk limits for C3/N4

Author: Lisa Pettyjohn

modules/persistent-storage-csi-gcp-hyperdisk-limitations.adoc

@@ -7,6 +7,8 @@
 = C3 and N4 instance type limitations
 The GCP PD CSI driver support for the C3 instance type for bare metal and N4 machine series have the following limitations:
 
+* You must set the volume size to at least 4Gi when you create hyperdisk-balanced disks. {product-title} does not round up to the minimum size, so you must specify the correct size yourself.
+
 * Cloning volumes is not supported when using storage pools.
 
 * For cloning or resizing, hyperdisk-balanced disks original volume size must be 6Gi or greater.
@@ -21,5 +23,8 @@ For information about creating the storage class, see Step 2 in Section _Setting
 ====
 ifndef::openshift-dedicated[]
 * Clusters with mixed virtual machines (VMs) that use different storage types, for example, N2 and N4, are not supported. This is due to hyperdisks-balanced disks not being usable on most legacy VMs. Similarly, regular persistent disks are not usable on N4/C3 VMs.
+
+* A GCP cluster with c3-standard-2, c3-standard-4, n4-standard-2, and n4-standard-4 nodes can erroneously exceed the maximum attachable disk number, which should be 16 (link:https://issues.redhat.com/browse/OCPBUGS-39258[JIRA link]).
+
+* link:https://cloud.google.com/compute/docs/disks/hyperdisks#limitations[Additional limitations].
 endif::openshift-dedicated[]
-* A GCP cluster with c3-standard-2, c3-standard-4, n4-standard-2, and n4-standard-4 nodes can erroneously exceed the maximum attachable disk number, which should be 16 (link:https://issues.redhat.com/browse/OCPBUGS-39258[JIRA link]).

modules/storage-persistent-storage-pv.adoc

@@ -165,7 +165,7 @@ ifdef::openshift-enterprise,openshift-webscale,openshift-origin[]
 |Fibre Channel  | ✅ | ✅ |✅ |  ✅ ^[3]^
 endif::[]
 ifndef::openshift-rosa[]
-|GCP Persistent Disk  | ✅ |✅ |   |   
+|GCP Persistent Disk  | ✅ ^[4]^ |✅ | ✅ | ✅ ^[4]^
 |GCP Filestore | ✅ | ✅ |✅ | ✅
 endif::openshift-rosa[]
 ifdef::openshift-enterprise,openshift-webscale,openshift-origin[]
@@ -181,7 +181,7 @@ ifdef::openshift-enterprise,openshift-webscale,openshift-origin[]
 |NFS  | ✅ | ✅ |✅ | ✅
 |OpenStack Manila  |  |✅ |  | ✅
 |{rh-storage-first}  | ✅ |✅ |  | ✅
-|VMware vSphere | ✅ |✅ |  |  ✅ ^[4]^
+|VMware vSphere | ✅ |✅ |  |  ✅ ^[5]^
 endif::[]
 |===
 [.small]
@@ -190,10 +190,25 @@ endif::[]
 
 2. Use a recreate deployment strategy for pods that rely on AWS EBS.
 
-3. Only raw block volumes support the ReadWriteMany (RWX) access mode for Fibre Channel and iSCSI. For more information, see "Block volume support".
+3. Only raw block volumes support the `ReadWriteMany` (RWX) access mode for Fibre Channel and iSCSI. For more information, see "Block volume support".
 
 ifndef::openshift-dedicated,openshift-rosa[]
-4. If the underlying vSphere environment supports the vSAN file service, then the vSphere Container Storage Interface (CSI) Driver Operator installed by
+
+4. For GCP hyperdisk-balanced disks:
+
+* The supported access modes are:
+** `ReadWriteOnce`
+** `ReadWriteMany`
+
+* Cloning and snapshotting is disabled for disks with `ReadWriteMany` access mode enabled.
+
+* You can attach a single hyperdisk-balanced disk volume in `ReadWriteMany` to a maximum of 8 instances.
+
+* You can only resize a disk in `ReadWriteMany` if you detach the disk from all instances.
+
+* https://cloud.google.com/compute/docs/disks/attach-disks[Additional limitations].
+
+5. If the underlying vSphere environment supports the vSAN file service, the vSphere Container Storage Interface (CSI) Driver Operator installed by
 {product-title} supports provisioning of ReadWriteMany (RWX) volumes. If you do not have vSAN file service configured, and you request RWX, the volume fails to get created and an error is logged. For more information, see "Using Container Storage Interface" -> "VMware vSphere CSI Driver Operator".
 endif::openshift-dedicated,openshift-rosa[]
 // GCE Persistent Disks, or Openstack Cinder PVs.