Samsung 840 White Paper page 28

based on what system component the user wishes to stress. The problem with this approach, however, is that most
applications are not very storage-centric. Since all SSDs are so fast in everyday tasks, these types of benchmarks are
less useful because they will show minimal differences between SSDs.
Interpreting Benchmark Results
Measurements
Among the many measurements you will come across, it is best to familiarize yourself with some of the most common:
Sequential Read speeds are reported in megabytes per second (MB/s) and indicate how fast the SSD will be at
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completing tasks like accessing large multimedia files, transcoding, game level loading, some types of game play,
watching and editing video. This is the speed at which the drive can read data from contiguous memory spaces.
Sequential Write speeds, also reported in megabytes per second (MB/s) indicate how fast the SSD will be at tasks
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like application installation and document backup. This is the speed at which the drive can write data to contiguous
memory spaces.
Random Read speeds, reported in Input/Output Operations Per Second (IOPS) indicate how fast the SSD will be at
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completing tasks like antivirus scans, searching for email in Outlook, web browsing, application loading, PC booting,
or working in Microsoft Word. This is the speed at which the drive can read data from non-contiguous memory
spaces.
Random Write speeds, also reported in IOPS, indicate how fast the drive will be able to complete tasks like
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downloading email, compressing files, or browsing the web. This is the speed at which the drive can write data to
non-contiguous memory spaces.
Some other common terminology you will encounter includes:
Idle Time, which is the period of time when an SSD is not handling requests to read or write data.
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Latency, which is the response time of the SSD, or the time between when you initiate a request to read or write
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data and when the SSD completes the request.
Queue Depth/Concurrent IOs, which is the outstanding (pending) number of IO requests that must be handled
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by the drive. Multiple requests are placed in a queue of a specific length, where they will wait for their turn to be
addressed by the SSD if another task is already underway. The most common queue depths to test are a Queue
Depth of 1, which is typical of light consumer workloads, and a Queue Depth of 32, which is representative of a
heavy workload as might be seen on a on a server (e.g. web server, database server, etc.). Where in that spectrum an
SSD will perform best varies based on the drive's firmware algorithm. Being optimized for high or low queue depths
or vice versus is not necessarily a bad thing, but rather a design decision.
Your Results May Vary
Remember that each of the measurements discussed above will vary from system to system. For example, the number
of IOPS possible on a given system will vary greatly depending on: the balance of read and write operations, the mix of
sequential and random patterns, the number of worker threads, the queue depth, and the data block sizes – and this is
without taking into account the effect of basic hardware configurations (microprocessor speed, DRAM size and speed,
chipset type and drivers, BIOS settings, etc.).
When working with Synthetic Benchmarking tools, keep in mind that Random Write performance will differ based on
the test range. For example, write tests with very small ranges may not be able to fully utilize the internal parallelism of
the NAND chips, resulting in low performance result.
Another major factor is whether or not an SSD uses compression technology. SSDs that use compression will suffer
significant performance drops (up to 90% of claimed maximum performance) when working with incompressible data
(e.g. JPEG photos, digital audio or video files, zipped files, etc.). Because everyday home and office PC users have and
use a considerable amount of this type of data in real-world usage scenarios, Samsung chooses not to use compression
technology in any of its current SSDs in favor of delivering industry-leading read and write performance with all data
types. This is also why Samsung uses incompressible (or Random) data when testing its SSDs.