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Oracle Database Tips by Donald Burleson
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RAC and
SSD
What is unique about RAC and SSD? RAC introduces a
new source of latency into the I/O picture. This new source of latency
deals with the cluster interconnect. As the latency of the cluster
interconnect increases, the ability to scale as well as the
performance of the cached data decreases. This decrease in performance
is especially noticeable in the case where all of the application data
is cached across the virtual memory area afforded by Oracle10g RAC.
Given this new source of latency, the effects of
the cluster interconnect in a fully cached environment must be
considered. Is the interconnect latency less than the latency of the
SSD? Is the interconnect latency higher than the SSD latency? These
are critical questions that will determine whether or not to force
cache transfer or force reads from the SSD as the primary means of
cache replacement for data. In all but the fastest interconnects, SSD
is faster.
What does SSD being faster than the interconnect
for data transfer indicate? Believe it or not, better performance may
be achieved by forcing the old disk ping behavior instead of a
transfer across the interconnect! Oracle has optimized the I/O path
more thoroughly than the memory paths taken by RAC in a transfer
situation, thus if the old slow disks are replaced with SSD
technology, better performance may result from reading from the SSD!
This behavior will be examined in the TPC-C results chapter.
The next step is to review the existing research
on SSD and see that other Oracle experts say about using SSD with
Oracle.
See
code depot for complete scripts
This is an excerpt from the book
Oracle RAC & Tuning with Solid State Disk.
You can get it for more than 30% by buying it directly from the
publisher and get immediate access to working code examples.
Market Survey of SSD vendors for
Oracle:
There are many vendors who offer rack-mount solid-state disk that
work with Oracle databases, and the competitive market ensures that
product offerings will continuously improve while prices fall.
SearchStorage notes that SSD is will soon replace platter disks and that
hundreds of SSD vendors may enter the market:
"The number of vendors in this category could rise to several
hundred in the next 3 years as enterprise users become more familiar
with the benefits of this type of storage."
As of January 2015, many of the major hardware vendors (including Sun and
EMC) are replacing slow disks with RAM-based disks, and
Sun announced that all
of their large servers will offer SSD.
Here are the major SSD vendors for Oracle databases
(vendors are listed alphabetically):
2008 rack mount SSD Performance Statistics
SearchStorage has done a comprehensive survey of rack mount SSD
vendors, and lists these SSD rack mount vendors, with this showing the
fastest rack-mount SSD devices:
| manufacturer |
model |
technology |
interface |
performance metrics and notes |
|
IBM |
RamSan-400 |
RAM SSD |
Fibre
Channel
InfiniBand
|
3,000MB/s random
sustained external throughput, 400,000 random IOPS |
|
Violin Memory |
Violin 1010 |
RAM SSD
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PCIe
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1,400MB/s read,
1,00MB/s write with ×4 PCIe, 3 microseconds latency |
|
Solid Access Technologies |
USSD 200FC |
RAM SSD |
Fibre Channel
SAS
SCSI
|
391MB/s random
sustained read or write per port (full duplex is 719MB/s), with
8 x 4Gbps FC ports aggregated throughput is approx 2,000MB/s,
320,000 IOPS |
|
Curtis |
HyperXCLR R1000 |
RAM SSD |
Fibre Channel
|
197MB/s sustained
R/W transfer rate, 35,000 IOPS |
Choosing the right SSD for Oracle
When evaluating SSD for Oracle databases you need
to consider performance (throughput and response time), reliability (Mean Time Between failures) and
TCO (total cost of ownership). Most SSD vendors will provide a
test RAM disk array for benchmark testing so that you can choose the
vendor who offers the best price/performance ratio.
Burleson Consulting does not partner with any SSD vendors and we
provide independent advice in this constantly-changing market. BC
was one of the earliest adopters of SSD for Oracle and we have been
deploying SSD on Oracle database since 2005 and we have experienced SSD
experts to help any Oracle shop evaluate whether SSD
is right for your application. BC experts can also help you choose
the SSD that is best for your database. Just
call 800-766-1884 or e-mail.:
 for
SSD support details. DRAM SSD
vs. Flash SSD
With all
the talk about the Oracle “flash cache”, it is important to note that there
are two types of SSD, and only DRAM SSD is suitable for Oracle database
storage. The flash type SSD suffers from serious shortcomings, namely
a degradation of access speed over time. At first, Flash SSD is 5
times faster than a platter disk, but after some usage the average read time
becomes far slower than a hard drive. For Oracle, only rack-mounted
DRAM SSD is acceptable for good performance:
|
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Avg. Read speed
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Avg. write speed
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Platter disk
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10.0 ms.
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7.0 ms.
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DRAM SSD
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0.4 ms.
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0.4 ms.
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Flash SSD
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1.7 ms.
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94.5 ms.
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