FS System: Low Performance Storage Tiers with Insufficient Drive Groups can Cause Latencies
Last updated on MAY 17, 2018
Applies to:Oracle FS1-2 Flash Storage System - Version All Versions to All Versions [Release All Releases]
Information in this document applies to any platform.
This document highlights potential performance issues when the low performance tier (Capacity HDD) does not have enough Drive Groups.
The issue has been seen on a system with a single Capacity HDD Drive Enclosure (2 Drive Groups). Most of the LUNs are set to use Auto-Tiering. The rest of the configuration has one Drive Group of Performance SSD and 6 Drive Groups of Performance Disk.
The slow response time is noticeable on the applications running on the hosts due to the latency on the Flash Storage.
On the FS1 GUI, under SAN -> Statistics and Trending -> LUNs, the IO Latency can be over 40 ms (milliseconds) for most of the LUNs.
The problem to a specific Drive Group can be isolated under System -> Reporting & Statistics -> Drive Group Statistics, double click on each Drive Group and measure the Total IO/s and Total Latency: the affected Drive Group(s) should report a latency of 100 ms or higher when the performance issue is observed.
Performance is affected when multiple access to Capacity HDD Drive Groups is done simultaneously, for example, weekly backups.
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