Have you tried

invoke-nasysstat -Disk *, should give you what you need

   TypeName: DataONTAP.Types.Perf.DiskPerfInfo

Name                MemberType    Definition
----                ----------    ----------
Busy                AliasProperty Busy = DiskUtilPercent
DiskRd              AliasProperty DiskRd = ReadBytesPerSecond
DiskWr              AliasProperty DiskWr = WriteBytesPerSecond
PendOps             AliasProperty PendOps = AveragePendingOps
QueueOps            AliasProperty QueueOps = AverageQueuedOps
RdLat               AliasProperty RdLat = ReadLatency
RdOps               AliasProperty RdOps = ReadOpsPerSecond
TotOps              AliasProperty TotOps = TotalOpsPerSecond
WrLat               AliasProperty WrLat = WriteLatency
WrOps               AliasProperty WrOps = WriteOpsPerSecond
Equals              Method        bool Equals(System.Object obj)
GetHashCode         Method        int GetHashCode()
GetType             Method        type GetType()
ToString            Method        string ToString()
AveragePendingOps   Property      System.Nullable[decimal] AveragePendingOps {get;set;}
AverageQueuedOps    Property      System.Nullable[decimal] AverageQueuedOps {get;set;}
Controller          Property      string Controller {get;set;}
ControllerTimestamp Property      System.Nullable[datetime] ControllerTimestamp {get;set;
Disk                Property      string Disk {get;set;}
DiskUid             Property      string DiskUid {get;set;}
DiskUtilPercent     Property      System.Nullable[decimal] DiskUtilPercent {get;set;}
ReadBytesPerSecond  Property      System.Nullable[decimal] ReadBytesPerSecond {get;set;}
ReadLatency         Property      System.Nullable[timespan] ReadLatency {get;set;}
ReadOpsPerSecond    Property      System.Nullable[decimal] ReadOpsPerSecond {get;set;}
Timestamp           Property      datetime Timestamp {get;set;}
TotalOpsPerSecond   Property      System.Nullable[decimal] TotalOpsPerSecond {get;set;}
WriteBytesPerSecond Property      System.Nullable[decimal] WriteBytesPerSecond {get;set;}
WriteLatency        Property      System.Nullable[timespan] WriteLatency {get;set;}
WriteOpsPerSecond   Property      System.Nullable[decimal] WriteOpsPerSecond {get;set;}