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Using solid-state disks to improve I/O speed on optimized databases

Oracle Tips by Mike Ault


Let's go solid

What I am referring to is the new trend (well, actually it has been around since the 90's) to move databases to solid state drives. In almost all cases this form of going solid leads to measurable performance improvements by elimination of the various latencies involved with the standard computer disk drive assemblies. Of course the removal of disk rotational and arm latencies is just one of the things that solid state drives bring to the table, the other is access to your data at near-memory speeds.

What solid state drives mean to an application is that if your application is currently suffering from IO problems some if not all of them are relieved. However, the benefits are a bit lop sided depending on the predominant type of IO wait your system is seeing. If your IO waits are due to contention during the retrieval of information (SELECT statements) then you can expect a dramatic increase in performance. In tests against standard disk arrays using the TPC-H benchmark I was able to achieve a 176 times performance increase for primarily retrieval based transactions. For what I refer to as IUD transactions (INSERT, UPDATE and DELETE) only a 30-60% performance improvement was shown.

Remember that retrieval requires no additional processing once the data location is returned from the search process, while IUD involves data verification via indexes, constraints and other internal processes that tend to slow down the process thus reducing the performance gains. Does solid state disk (SSD) technology eliminate waits? Of course not, what it does is reduce their duration. For example, looking at load times:
 


Load Graph Using SSD


You can from the graph that load times for standard disks was on the average about 30% slower than the load times for an equivalent SSD drive array.

However looking at query response time, we see an entirely different picture:


SSD Queries

When we compare the SSD times with the same queries, same OS settings and same layout on standard drives, we see a dramatic difference (notice the scale on this next graph is logarithmic, not linear):


ATA Queries

The second graph really drives home the point, I had to make it logarithmic because of the great differences in time duration for the various queries when going to disks. What required a couple of hours (running the 20+ base queries) on SSD required 3 days on the average for the ATA drives.

Of course we don't remove the IO waits by using SSD, their duration is simply reduced to the point they are not a big factor anymore. Of course, for scalability and such you still will need to tune SQL.

Some how, I see going solid in our future.  For a complete copy of the testing, see the new book "Oracle tuning with solid-state disk" and my newest book, "Oracle RAC and Grid tuning with 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.

 

 

 

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.

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