Choosing RAID disk configuration for Oracle
Oracle Tips by Burleson Consulting
There is a great debate about the "proper" storage subsystem for
Oracle databases, and the discussion continues to evolve as the
disk/SSD technology changes and large RAM data buffers become more
While CPU and Network latencies
drop dramatically every year, disk access speed has not changed in
the past decade and remains in the range of 10-50 milliseconds.
Many disk vendors have employed on-board RAM caches to provide the
illusion of faster disk access speeds, but the ancient platters of
magnetic-coated media will soon be as obsolete as punched cards.
RAID Issues and Oracle
RAID5 has always been
problematic for OLTP Oracle databases. While RAID5 is a great
solution for read-only systems, the overhead of updates has made the
I/O subsystem quite slow for databases with active DML. Vendors have
improved RAID5 for high DML systems.
Starting in Oracle10g we see
that Oracle has codified their storage recommendations within the
Oracle 10g Automatic Storage Management (ASM). Oracle
officially recommends the SAME approach (Stripe And Mirror
Everywhere), which is essentially RAID 1+O with segregation of
undo/redo and rollbacks on separate spindles.
The use of Solid-State disk
(a.k.a. RAM-SAM, RAM-disk) is rapidly becoming practical for Oracle
databases. As RAM prices continue to fall, SSD is becoming a
reliable and cost-effective alternative to magnetic-coated disk
platters. IDC projects that the SSD market could reach $2
billion in 2004 and there is no-doubt that SSD will soon replace the
archaic platter-based disks for Oracle storage.
On most I/O-bound Oracle
systems, implementing SSD will provide stunning performance
improvements, often 10x to 30x faster. While still moderately
expensive (about $1k/gigabyte), many Oracle shops with large
database will selectively implement SSD, using solid-state disk for
their redo, undo and TEMP tablespaces.
SSD is also becoming a popular
alternative to expensive Oracle application tuning. An
I/O-bound Oracle database with a poorly-written application can be
quickly moved to SSD within hours, and performance can be
significantly improved. According to
this article in SearchStorage.com:
"In applications where I/O
is unbalanced, the most frequently accessed files, also called "hot
files," make up less than 5% of an application's total data, but eat
up more than 50% of the I/O activity. Moving hot files to SSD file
cache frees up servers and boosts performance."
Remember, SSD is only
beneficial for Oracle shops that are I/O-bound, and an analysis is
required to determine where SSD is beneficial. I/O contention
can be easily located with OracleSTATSPACK or Oracle10g AWR data,
and this analysis allows the Oracle DBA to appropriately place SSD
where it is needed most.
Market Survey of SSD vendors for
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:
||performance metrics and notes
sustained external throughput, 400,000 random IOPS
1,00MB/s write with ×4 PCIe, 3 microseconds latency
Solid Access Technologies
sustained read or write per port (full duplex is 719MB/s), with
8 x 4Gbps FC ports aggregated throughput is approx 2,000MB/s,
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.:
SSD support details.
vs. Flash SSD
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
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