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Oracle Database Tips by Donald Burleson
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A Review
of Existing SSD Research Findings
Different researchers are coming to different
conclusions about the applicability of SSD to Oracle systems. There
are three research papers on SSD, and each arrives at similar
conclusions about the use of SSD with Oracle. Complete references are
included in the reference section. The following sections provide a
quick look at the summary findings from each study.
James Morle
According to Morle in 2002, SSD is great for
Oracle redo logs, undo tablespace, rollback segment tablespace in
Oracle8i, and the TEMP tablespace.
He notes that for rollback segments, SSD is a great help:
"This is where SSD can
help out. By deploying a single SSD, all redo logs can be located
away from the RAID 1+0 array, whilst providing low latency writes
and high bandwidth reads (for archiving)."
Morle also asserts that full caching of a database
on SSD may not improve performance:
"If the whole database
were running from SSD, there would be enormous pieces of unnecessary
work going on, such as:
Management of the
buffer cache
Context switches into
kernel mode to perform I/O
Conversion of the
request into SCSI/Fibre Channel
Transmission across
the SAN
And all the way back
again
In comparison to disk
I/O, this whole process is stunningly fast. In comparison to just
reading the data straight from user space memory, however, it is
incredibly slow!"
Morle notes that a typical OLTP system has a
working set of frequently referenced data blocks, and those might be
good candidates for SSD. For DSS and Data Warehouse systems, Morle
advocates moving the current table partitions onto SSD devices,
leaving the others on traditional disk.
Dr. Paul Dorsey
In another landmark SSD study in 2004, Dr. Paul
Dorsey showed that the data transfer rates for SSD's are always better
than traditional disk:
|
DEVICE |
TEST#1: BUFFERED READ |
TEST #2: SEQUENTIAL READ |
TEST #3: RANDOM READ |
TEST #4: BUFFERED WRITE |
TEST #5: SEQUENTIAL WRITE |
TEST #6: RAMDOM WRITE |
|
RamSan |
95 |
98 |
98 |
86 |
84 |
82 |
|
IDE |
85 |
40 |
6 |
65 |
38 |
11 |
|
SCSI |
65 |
33 |
9 |
49 |
33 |
11 |
Dr. Dorsey concludes:
"Technologically, SSD
is one of the best sources of performance improvement for an Oracle
database if you have a typical OLTP system including many
transactions which access different small amounts of random data and
lots of users.
SSDs may also improve
data warehouse applications because of the improved query
performance. There is no generic answer for all questions, but solid
state disks represent another way of thinking about managing
enterprise-wide databases. "
Woody Hutsell
The Texas Memory Systems whitepaper titled
Faster Oracle Database Access with
the RAMSAN-210 (Hutsell, 2001) concludes that certain types of
Oracle databases will always benefit from SSD:
There are some databases that should have all of
their files moved to SSD. These databases tend to have at least one of
the following characteristics:
-
:
DBA's managing databases that are being hit by a large number of
concurrent users should consider storing all of their data on SSD.
This will ensure that storage is not a bottleneck for the
application and maximize the utilization of servers and networks.
I/O wait time will be minimized and servers and bandwidth will be
fully utilized.
-
:
For some databases, it is impossible to identify a subset of files
that are frequently accessed. Many times these databases are
effectively large indices.
-
:
Given the fixed costs associated
with buying RAID systems,
it is often economical to buy a SSD to store small to medium sized
databases. A RamSan-210, for example, can provide 32GB of database
storage for the price of some enterprise RAID systems.
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
|
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
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Avg. write speed
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Platter disk
|
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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