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SSD performance is very low in 5500V3 when use eDesigner for design and planning

Publication Date:  2017-11-07 Views:  33 Downloads:  0
Issue Description

A channel engineer made a temporary solution on 5500V3 storage, but he found a strange behavior.

Storage configuration:

OceanStor5500 V3; Dual-Controller; 48GB Cache,25*2.5"; SAN

OLTP; read ratio: 70%; I/O Block Size: 8KB

Value-Add feature:SmartTier

Hotspot Intensity Ratio Calculation Method use default: Conversion By Capacity Ratio

The performance of single tier is below:


 But, if we deactivate SmartTier feature, 5 * 900GB SSD can reach 26729 IOPS with the same configuration.

Solution

When you activate SmartTier feature on eDesigner, also on the real IT infrastructures, there's a critical parameter called Hotspot Intensity Ratio. It means proportion of IOPS assigned to the SSDs, because, only hotspot data will be migrated to high performance tier.

For "Hotspot Intensity Ratio Calculation Method" on eDesigner, there're two options, the default method is "Conversion By Capacity Ratio". In this option, the eDesigner give a experienced hotspot intensity ratio based on service model and capacity ratio of SSD tier. Also, customer can specify a customized  "Hotspot Intensity Ratio".

For example, if the "Hotspot Intensity Ratio" is 50%, it means only 50% IOPS assigned to SSDs, and the other 50% assigned to SAS and NL-SAS tier. So, if the total IOPS of SAS tier and NL-SAS tier is 3000, SSD tier can also assigned 3000 IOPS, even SSD tier can carry much higher performance.

In this case, the capacity ratio of SSD tier is 8.08%. So, the eDesigner finally got "Hotspot Intensity Ratio" as 41.32%. That's why SSD can only 1910 IOPS in final result.

END