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Oracle Database Tips by Donald Burleson |
Improving I/O Speed is Not a
Silver Bullet
SSD and RAM buffer caching are only
important to I/O-intensive Oracle databases. If an Oracle database
is constrained by other environmental factors such as CPU or
network, speeding up the I/O subsystem will not result in any
appreciable performance gains. To learn about databases resource
bottlenecks, the DBA need only display the top-5 timed events from
STATSPACK.
The following is a typical OLTP database
where I/O delay is the main source of wait time. I/O comprises more
than 70% of total elapsed time.
Top 5
Timed Events
~~~~~~~~~~~~~~~~~~
% Total
Event Waits
Time (s) Ela Time
--------------------------- ------------ ----------- ------
db file
sequential read 2,598 7,146 48.54
db file
scattered read 25,519 3,246 22.04
library
cache load lock 673 1,363 9.26
CPU
time 1,154 7.83 6.21
log file
parallel write 19,157 837 5.68
Again, it is critical to note that
additional RAM resources may not have any appreciable effect on
databases that are not I/O intensive. For example, some scientific
Oracle databases only read a small set of experimental results and
spend the majority of database time performing computations. The
output of such a database is shown below:
Top 5
Timed Events
~~~~~~~~~~~~~~~~~
% Total
Event Waits Time (s) Ela
Time
---------------------------------- ------------ ----------- -----
CPU
time 4,851 4,042 55.76
db file
sequential read 1,968 1,997 27.55
log file
sync 299,097 369 5.08
db file
scattered read 53,031 330 4.55
log file
parallel write 302,680 190 2.62
In this example, CPU time is the primary
source of database delay, and improving the speed of the I/O with
SSD may not have an appreciable effect on overall Oracle
performance.
One must be cognizant that it is foolish to
focus solely on minimizing physical disk I/O. For databases with
sub-optimal SQL statements, poor performance is commonly combined
with a high data buffer cache hit ratio and little disk I/O. For
these databases, the root cause of the performance problem is
excessive logical I/O, whereby the sub-optimal SQL rereads data
blocks over and over from the RAM data buffers.
The above book excerpt is from:
Oracle RAC
& Grid Tuning with Solid State Disk
Expert Secrets for High Performance Clustered Grid Computing
ISBN:
0-9761573-5-7
Mike Ault, Donald K. Burleson
http://www.rampant-books.com/book_2005_2_rac_ssd_tuning.htm
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
|
PCIe
|
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:
|
|
Avg. Read speed
|
Avg. write speed
|
|
Platter disk
|
10.0 ms.
|
7.0 ms.
|
|
DRAM SSD
|
0.4 ms.
|
0.4 ms.
|
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Flash SSD
|
1.7 ms.
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94.5 ms.
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