VPLEX: Distributed Device experiencing performance issues
Summary: VPlex Distributed Device experiencing performance issues
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Not all product versions are identified in this article.
Symptoms
Hosts are experiencing high write latency on VPlex distributed devices
Cause
Regarding distributed devices, the VPlex confirms that any write I/O is committed to BE storage on both sites before returning acknowledgement to the host.
If the inter-cluster FC/IP WAN network is experiencing network congestion, it will result in increasing the round trip time of I/O packets which is causing the performance issue.
On the other hand VPlex always serves the read I/Os from the global cache if available or local BE array.
VPlex best practice indicates that RTT between VPlex clusters shouldn't exceed 5 ms to provide the best performance and an RTT of 1 ms for a campus wide network.
If the inter-cluster FC/IP WAN network is experiencing network congestion, it will result in increasing the round trip time of I/O packets which is causing the performance issue.
On the other hand VPlex always serves the read I/Os from the global cache if available or local BE array.
VPlex best practice indicates that RTT between VPlex clusters shouldn't exceed 5 ms to provide the best performance and an RTT of 1 ms for a campus wide network.
Resolution
1. Check the firmware logs you find com/21 and com/24 events indicating network congestion.
example:
128.221.253.36/cpu0/log:5988:W/"00601661de2210138-2":141384:<4>2017/04/12 09:16:16.10: com/21 COM IO took 1.047 sec to complete (limit 900.000 msec). Type message, uuid 0x4xxxxxx, transport scsi, msg_len 72
128.221.252.38/cpu0/log:5988:W/"0060165322f014450-2":2170302:<3>2016/10/22 23:29:35.92: com/24 86 long-latency IOs in past hour (Msg: 86) Printed up to 100.
128.221.253.36/cpu0/log:5988:W/"00601661de2210138-2":141384:<4>2017/04/12 09:16:16.10: com/21 COM IO took 1.047 sec to complete (limit 900.000 msec). Type message, uuid 0x4xxxxxx, transport scsi, msg_len 72
128.221.252.38/cpu0/log:5988:W/"0060165322f014450-2":2170302:<3>2016/10/22 23:29:35.92: com/24 86 long-latency IOs in past hour (Msg: 86) Printed up to 100.
2. Confirm that all WAN com ports are up and SFP's power is greater than 200 uW, if not you should follow KB https://support.emc.com/kb/468785
3. If the VPlex is FC metro configuration and the WAN FC switches are Dell EMC supported, you should follow KB https://support.emc.com/kb/335508 to collect the switch logs and engage Dell EMC support.
4. If the VPlex is IP metro configuration, validate the IP network health to see what is causing this congestion.
3. If the VPlex is FC metro configuration and the WAN FC switches are Dell EMC supported, you should follow KB https://support.emc.com/kb/335508 to collect the switch logs and engage Dell EMC support.
4. If the VPlex is IP metro configuration, validate the IP network health to see what is causing this congestion.
Affected Products
VPLEX SeriesProducts
VPLEX GeoSynchrony, VPLEX Series, VPLEX VS1, VPLEX VS2, VPLEX VS6Article Properties
Article Number: 000167575
Article Type: Solution
Last Modified: 28 Oct 2025
Version: 3
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