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New flash drive disks for Oracle

Oracle Database Tips by Donald BurlesonSeptember 26, 2015

As disk and RAM prices continue to fall at an astonishing rate, many Oracle shops are removing their I/O bottlenecks with RAM disk, solid-state flash memory which can read and write data hundreds of times faster then the old-fashioned spinning platters from the 1960's.

As of 2015, SSD RAM disk costs less than a platter disk from the 1990's, and Oracle shops across the globe are switching to solid-state storage for their mission critical data.  At a cost of only $150 per gigabyte, a new generation of SSD flash disks are affordable for almost any Oracle shop.

It's important not to confuse the PC-based flash technology (like PC flash drives) with the industrial-strength SSD that is used for Oracle databases.  The SSD used for Oracle is extremely fast and getting cheaper every year and it's only a matter of time before all Oracle databases will reside on solid state disks. 

It's important for all Oracle professionals to learn about solid-state disk to understand how I/O bottlenecks will soon become a thing of the past.  Let's take a close look at this emerging technology.

Inside the next generation of data storage hardware

The ancient platter-based disks from the 1960's will soon join paper tape and punched cards in the annals of IT history.  As prices of RAM and flash disks fall to affordable levels, the majority of Oracle database will run entirely solid-state, with the only physical I/O being external background writes from the solid-state disk (SSD) to it's backup storage disks.  Oracle with SSD offers blistering data access speeds and it can save shops from expensive manual tuning efforts.

As of September 2015, you can buy 100 gigabytes units of SSD for less then $90k, making RAM-based SSD an extremely affordable option for smaller database that are plagued with disk I/O bottlenecks.  For larger Oracle databases, the new TMS RAM-SAN 500 offers up to two terabytes of fast cached Flash solid state disk for only $150 per gigabyte (cached flash systems use a combination of DDR RAM as cache and Flash memory as persistent high density storage.

When choosing an SSD hardware vendor, many risk-averse IT managers choose the industry leader.  The undisputed leader in the realm of super-fast RAM disks is Texas Memory Systems (TMS), one of the largest providers of SSD for Oracle.  I've worked with many shops who use TMS SSD for their Oracle systems and their response has been uniformly positive.  But it just keeps getting better, a revolutionary new technology that will forever change the landscape of corporate database management.  Let's take a closer look.

The latest SSD for Oracle

 

In September 2015, TMS introduced the next generation of solid-state flash drives for Oracle databases, dubbed the RamSan-500.  Offered in one and two terabyte units, this is the disk platform of choice for mission-critical Oracle databases that must meet strict response time SLA's.   The main difference between this system and others that TMS has done is that this system uses a big capacity of Flash memory as the storage media.  Flash memory is best known for its fast read performance.  Putting this flash memory behind a large RAM cache provides a great combination of:  high performance (for reads and writes), high density, low power consumption and improved cost per capacity.

 

Here are the technical details for the latest Oracle flash drive technology:

 

The RamSan-500, TMS' ninth generation solid state disk, is the most important advance in solid state disk storage in the last twenty years. The system is designed for high IO data warehousing, high bandwidth data acquisition, and rich media environments. The RamSan-500 is a hybrid of DDR RAM and Flash Memory (NAND-SLC).

 

According to eWeek, the TMS SSD flash disks have many appealing features:

 

"The new RamSan-500 pairs DDR caching, which provides high write performance, with flash memory, which offers good read performance. It provides another option for organizations that need better performance but can't afford to put all of their capacity into DDR solid state disk."

 

Leveraging the flash drives for Oracle

 

With this rapid decline in hardware costs, a shift has occurred within the Oracle community.  Instead of costly and time-consuming tuning to reduce physical disk I/O, many shops find that it is cheaper and less risky to use solid-state disks in lieu of expensive and risky human tuning.

 

Does it make sense to "throw hardware" at an Oracle performance problem and ignore the root cause of the problem?  Like all Oracle questions, the answer is "it depends", and it depends on the exact nature of the performance issue.  If the root cause requires an expensive and risky redesign or re-writing thousands of lines of code, the answer may be "yes".

 

 

 

 

When to apply fast hardware to an Oracle performance problem

When does it make sense to throw hardware at an Oracle performance problem?  Throwing hardware makes great sense for the following types of Oracle performance problems, even though it does address the root cause of the performance issue:

  • Over-normalized design - A legacy 3NF database (with high DML, prohibiting materialized views) can run faster with SSD, a far less expensive solution that a full re-design to introduce redundancy into the data model.  Introducing redundancy into a 3NF model can greatly reduce table joins, and reduce server stress. 
     
  • sub-optimal application code - It's not hard to find poor Oracle code, as noted by the entertaining Oracle WTF site.  Those offshore "bargain" systems can be made to run faster, without the expense and risk of re-writing thousands of lines of code.  Some examples of bad code include large systems where optimizing the code (to fix the root cause) would take months and cost hundreds of thousands of dollars.

The new cached Flash solution is a great fit for larger tablespaces in read-intensive OLTP and Data Warehouse environments.  Performance for a flash memory based system is not as fast as it is for an all RAM based system, but it can still shave milliseconds off response times for database reads enabling big improvements in application performance.  For smaller databases and redo logs, RAM based solid state disks will still be the best choice.

I/O bottlenecks can be sporadic and isolated in several areas of Oracle, especially high-impact areas such as redo log files.  Once you have tuned all SQL impacting the data files, solid-state disk (SSD) can be a great solution.  For Oracle, SSD can do I/O 300x-2,000x faster than platter disk (Texas Memory Systems sells 100 gig for only $90k). For details, see my book "Oracle Solid State Disk Tuning:  High Performance Oracle Tuning with RAM disk".

Tuning I/O bottlenecks in RAC with RAM-SAN is more challenging, and I have conducted benchmarks that suggest that SSD is a Godsend for RAC when combined with specially-designed, tiny data buffers on each node. See my book "Oracle RAC & Grid Tuning with Solid State Disk: Expert Secrets for High Performance Clustered Grid Computing" for details on RAC tuning with Solid-State Disk.

The performance of SSD

In my reproducible benchmarks of SSD vs. platter disks, the response time benefits of using SSD with Oracle are amazing with blistering speeds that result in up to a 300x speed improvement. 

According to the book "Oracle Solid State Disk Tuning", smaller solid-state RAM disks have far less bandwidth issues because the RAM architecture of SSD allow high concurrent access that is impossible on a mechanical platter.

This issue of single channel access also imposes a bottleneck on Oracle disk devices, and the large disks (over 144 gigabytes) often perform more slowly for high concurrent access than their smaller predecessors.

  • Oracle's standard SAME (Stripe and Mirror Everywhere, RAID 10) is largely useless for load balancing if the whole database resides on just a few physical disks.
     

  • Seek delay (movement of the read-write heads) composes over 80% of disk access latency, and high concurrent requests against large devices make them very slow.

Disk enqueues can occur when the disk is unable to quickly service concurrent requests.  Super-large disks can be problematic, and the most popular Oracle data files can be placed on the middle absolute track of the device to minimize read-write head movement.

As a result of this trend, many Oracle professionals experience external I/O waits and they see that the top-5 waits events (from a STATSPACK or AWR Report) show "db file sequential reads" and "db file scattered reads" as a main system bottleneck.

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.

 

Books on Oracle SSD:

 

My related  notes Oracle SSD:


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.

 


 

 

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