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Be Careful of Storage Performance Track .pdf

Original filename: Be Careful of Storage Performance Track.pdf
Author: Wangjiaxin (Jacky, Dorado)

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Be Careful of Storage Performance Track

Excellent performance is an everlasting pursuit for storage system vendors. Vendors use
different performance parameters to promote product performance, such as 100% cache
hit ratio (maximum IOPS), 256 KB I/O bandwidth, and 100% write latency. All vendors
want you to believe that they can provide the highest performance and can easily handle
business pressure during peak hours. You may want to know how to identify all-flash
arrays that truly have high performance from amongst a huge number of potentially
misleading promotions.

Track 1: 100% cache hit ratio

When promoting storage performance, many vendors often boast they can achieve "100%
cache hit". This means that all data is stored in memory, instead of being stored
permanently. A criterion to determine whether IT architecture is high performance is to
check whether it stores the most frequently accessed data in the location that has the
fastest response times.

This essentially means that it is almost impossible to have a 100% catch hit ratio in
customer environments. This is because all-flash storage applies to not only different
industries but also to varying business models within industries. Therefore, such a claim
must be taken with a grain of salt, and customers should thoroughly check their needs
against what the product can offer.

Trick 2: 100% read performance

Mainstream SSDs offer high performance in data reads, but their write performance is
lacking because each time data is written, SSDs erase data from a NAND before writing
new data. This process is called "Program/Erase", which takes 1 ms to 2 ms in MLC/TLC
NAND flash, and leads to huge performance differences in data reads and writes.

Program/Erase in NAND flash

SSDs often reserve a large amount of over-provisioning space and the "Erase/Program"
process is not required every time data is written onto SSDs. Generally speaking, SSD
performance suffers more in mixed read and write scenarios than in read-only scenarios.
Therefore, real-life performance values must reflect customer business models (such as 8
KB I/O data blocks, read/write ratio 7:3, and RAID 5/6 groups), instead of boasting the
value of 100% read performance.

Data models in typical scenarios

Trick 3: Performance stability

Many vendors only promote reference values that are achieved using a specific model
and under certain conditions, which does not show their products' stability.

The stability of storage performance is critical, especially during service pressure changes
and in complex service environments. When choosing storage SLA, customers regard
stability as one of the most important indicators, encouraging vendors to produce limited

results, which mislead their customers. Stability indicates that response times of 99% of
services must remain stable under certain conditions. If services fluctuate, user
experience suffers. However, most customers are, unfortunately, unaware of this issue.
flash storage

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