SAN increased latency with low throughput from VAAI Copy Offload
Applies to
- ONTAP 9
- VAAI Copy Offload
- Data ONTAP 8 7-Mode
Issue
- System Manager dashboard displays a high LUN latency without a significant increase in IOPS or throughput.
- High latency is mostly with SAN Other operations.
- QOS statistics list high latency from Data layer.
::> qos statistics volume latency show -vserver SVM1 -volume volume1
Workload ID Latency Network Cluster Data Disk QoS Max QoS Min NVRAM Cloud FlexCache SM Sync VA AVSCAN
--------------- ------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
volume1 5935 321.31ms 143.00us 5.00us 321.15ms 0ms 0ms 0ms 10.00us 0ms 0ms 0ms 0ms
volume1 5935 200.02ms 132.00us 5.00us 199.88ms 0ms 0ms 0ms 9.00us 0ms 0ms 0ms 0ms
volume1 5935 263.63ms 76.00us 14.00us 263.52ms 18.00us 0ms 0ms 4.00us 0ms 0ms 0ms 0ms
volume1 5935 289.97ms 132.00us 4.00us 289.82ms 0ms 0ms 0ms 9.00us 0ms 0ms 0ms 0ms
volume1 5935 340.44ms 128.00us 7.00us 340.29ms 0ms 0ms 0ms 7.00us 0ms 0ms 0ms 0ms
-
HDD read/write
orSSD read/write
is much higher thanFCP in/out
oriSCSI in/out
from thesysstat -x
outputs.- If VAAI Copy Offload source volume and destination volume are from the same node,
Net in/out
is as low asFCP in/out
oriSCSI in/out
insysstat -x
. - If VAAI Copy Offload source volume and destination volume are from different nodes,
Net in/out
is as high asHDD read/write
orSSD read/write
insysstat -x
.
- If VAAI Copy Offload source volume and destination volume are from the same node,
Example 1:
Notes:
- iSCSI + HDD
- VAAI Copy Offload Source volume and Destination volume on the same node
Net in/out
&iSCSI in/out
are both much lower thanHDD read/write
Example 2:
Notes:
- FCP + SSD
- Source volume and Destination volume are from different nodes
- This is the Source node
Net out
is as high as SSD read, and they are both much higher thanFCP out
Example 3:
Notes:
- FCP + SSD
- Source volume and Destination volume are from different nodes
- This is the Destination node
Net in
is as high asSSD write
, and they are both much higher thanFCP in