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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 common. 

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 greatly 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.

Solid-state disk

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 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.

Flash SSD    

 1.7 ms.

 94.5 ms.

 


 
If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

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