Ssd Performance On Ds5000 Storage Subsystems - IBM Midrange System DS4000 Series Hardware Manual
Midrange system storage ds4000/ds5000 series
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Also See for Midrange System DS4000 Series:
- Hardware maintenance manual (184 pages) ,
- Installation and user manual (84 pages) ,
- Planning and installation manual (44 pages)
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Write caching
Write caching will always be enabled for SSDs. Write caching improves performance and
extends the life of the SSD
Background media scan
You cannot enable background media scans on SSDs. Background media scans are not
needed for SSDs because of the high reliability of SSDs. Furthermore, background media
scans will be detrimental because they increase wear on the SSDs.
SSD performance on DS5000 storage subsystems
In addition to capacity growth, there is an increasing need to process data quickly. In some
cases, the high volume of users accessing a database can result in the need for a high IOPS
rate. In other cases, there is a need to quickly process data, and to index the incoming
streams to allow high-speed searches and retrieval of needed records. Within the database or
file system middleware, there are directories, lock managers, and access control records that
must be accessed and updated at rates that scale with the size of the data or the number of
clients being served.
A need for high performance disks
There are some applications that simply cannot be run fast enough to satisfy business needs.
These include trading algorithms, complex simulations in aerospace or pharmaceutical
design, and security video analysis. Online transaction processing (OLTP) systems are the
classic example of these applications. Many of these usages of data create a need to operate
at high speed, often on indices or subsets of larger collections of information. In cases where
the IOPS performance of the storage is the system bottleneck, there is a high value in faster
storage and using SSDs.
Over the years, HDDs have maintained a dramatic rate of improvement in terms of dollar per
gigabyte, which has enabled data center administrators to keep up with storage capacity
demand without greatly increasing expenses. HDDs have also performed relatively well in
achieving improvements to sustained bandwidths (GBps) with recent15K RPM drives
advertising greater than 170 MBps speeds. But the rate of improvement in IOPS has lagged
far behind other system elements. While the dollar to gigabyte ratio has improved at a rate of
50 percent per year or more over the last decade, IOPS has only increased at a rate of 5
percent per year, and has slowed even further in recent years.
This parameter of performance is dominated by the mechanical elements of the drive: the
drive's rotational speed and the seek time of the arm. Substantial improvements for each
drive form factor (for example, 3.5") are no longer attainable. Although some minor
improvement are possible by using smaller drives (for example, 2.5" at 15K RPM), this comes
at a higher dollar to gigabyte cost. This lack of improvement in IOPS means that HDDs are
actually getting worse in access density as defined by IO per GB per second (I/O / GBps).
Storage management, performance, and cost are big issues in the database world. Database
workloads, both transactional and data warehousing, typically require lots of HDDs for I/O
performance, both IOPS and bandwidth. Traditional enterprise HDDs, including the 15K RPM
HDDs, are limited by the rate of head movement and deliver random I/O performance of
approximately 150 -175 IOPS with a latency of about 5 -7 ms and sequential scan bandwidth
of about 30 - 60 MBps for most database workloads. Write-intensive batch jobs are under
pressure to complete within the increasingly shrinking time-window, leading to reduced
uptime for transactional database systems.
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IBM Midrange System Storage Hardware Guide
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