Network latency in a Fibre Channel SAN environment
Applies to
- NetApp FAS/AFF systems
- Fibre Channel Protocol (FCP)
- VMware ESXi
- Linux
- Windows
Issue
- Workloads on hosts accessing LUNs via FCP incur significant application and client latency
- ONTAP has low latency (less than 5 milliseconds) in latency counters
- In SAN environments when the storage gets a request from a host, an internal timer starts and tracks how long the operations takes in each of the storage delay centers, all of which are internal except for "Network"
- The timer does not stop until the request has been serviced by storage and receives an acknowledgement from the host
- This delay incurred while waiting for host acknowledgement is observed as "Network" latency and hence considered external to storage controller
- Below errors may be observed in EMS logs for FC ports but will not show up in all cases.
Thu Oct 19 07:08:40 +0100 [NetApp-01: fct_tpd_work_thread_0: fcp.io.status:debug]: STIO Adapter:0e AEN 0x8048 (RECV_ERROR) MboxStatus1 0xfffe MboxStatus2 0x2
Thu Oct 19 08:16:30 +0100 [NetApp-01: fct_tpd_work_thread_0: fcp.io.status:debug]: STIO Adapter:0e AEN 0x8048 (RECV_ERROR) MboxStatus1 0xfffe MboxStatus2 0x1
Thu Oct 19 08:55:45 +0100 [NetApp-01: fct_tpd_work_thread_0: fcp.io.status:debug]: STIO Adapter:0f AEN 0x8048 (RECV_ERROR) MboxStatus1 0xfffe MboxStatus2 0x1
- Network latency in SAN environment is seen in the
Network
delay center orNetwork
in Active IQ Unified Manager (AIQUM) but not inNetwork Processing
under the Cluster Components volume view
Example:
qos statistics volume latency show
shows high latency in the Network
column for three SAN workloads
cluster::> qos statistics volume latency show -node san_node1
Workload ID Latency Network Cluster Data Disk QoS NVRAM Cloud ----------- ------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- volume_SAN1 17882 20.51ms 20.51ms 0ms 0ms 0ms 0ms 0ms 0ms volume_SAN2 5232 15.00ms 15.00ms 0ms 0ms 0ms 0ms 0ms 0ms volume_SAN3 17160 16.00ms 16.00ms 0ms 0ms 0ms 0ms 0ms 0ms