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SSD DC S3500 Workload Characterization in RAID Configurations

December 2013 White Paper

329903-001US 7

4.2 Queue Depth and Latency

Latency – The amount of time needed to service one outstanding IO to the drive,

measured in milliseconds (ms) or, with SSDs, microseconds (µs).

The Intel

SSD DC S3500 Series supports a maximum queue depth of 32 per drive. In a

RAID array, the queue depth is multiplied by the number of drives in the RAID set.

Example: In a RAID 5 set of 8 drives, the maximum total queue depth would be 256 (8

X 32). As more commands are queued in the SSD, average latency is impacted. Our

internal testing indicates that average latency increases sharply with queue depths

beyond 8. However, these high queue depths can increase IOPS with read intensive

workloads.

Obtaining the best performance for a particular application requires balance. The

challenge is to achieve high speed or IOPS at an acceptable latency level. This white

paper presents lower queue depths of 1, 2, 4 and 8 per drive. The results shown

demonstrate favorable speed and IOPS generation without pushing latency to extreme

levels.

4.3 Why Mixed Workload Is Important

Mixed random workloads are predominant in data center and enterprise applications.

Intel SSDs have been deployed in a variety of these applications ranging from content

delivery and video on demand networks, to Internet datacenter portals and database

management servers. Although these applications see unique IO traffic across the

storage drive, there are commonalities in their usage of random and read/write mixed

workloads.

Table 1 shows an overview of transfer sizes, read/write mixes and randomness in

commonly used workloads in data center applications. These are based on commonly

available industry information and information available through such benchmarks as,

TPC-C, TPC-E, TPC-H, and TPOX, which attempt to mimic these real world applications.

Table 1. Typical Mixed Workloads in Data Center Applications

Application Transfer Size %Random %Read

Web-Servers

4KB/8KB/16KB+

~75%

~95%

Exchange Email

4KB

~95%

~70%

Database OLTP

4KB/8KB

~95%

~70%

Decision Support

16KB+

~95%

Video On Demand

16KB+

~95%

Search Engine

4KB/8KB/16KB

~95%

Cache

16KB+

~95%

Content Delivery Network

16KB+

~95%

~70%-95%

Based on these usage trends, small transfer sizes–ranging from 4KB to 16KB and

above–are common in enterprise and data center applications. Also, much emphasis is

placed on random accesses, and although there are varied levels of read and write

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