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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 arrive at similar conclusions about the use of SSD with Oracle.  Complete references are included in the References section at the end of this section.  Here is a summary of the findings from each study.

James Morle

According to (Morle, 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 maintains 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 SSD data transfer rates 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: Random 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

In his Texas Memory Systems whitepaper titled Faster Oracle Database Access with the RAMSAN-210 (2001), Hutsell 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 solid state disk. These databases tend to have at least one of the following characteristics:

High concurrent access. Databases that are being hit by a large number of concurrent users should consider storing all of their data on solid state disk. This will make sure 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.

Frequent random accesses to all tables. For some databases, it is impossible to identify a subset of files that are frequently accessed. Many times these databases are effectively large indices.

Small to medium size databases. Given the fixed costs associated with buying RAID systems, it is often economical to buy a solid state disk 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.


The above book excerpt is from:

Oracle Solid State Disk Tuning

High Performance Oracle tuning with RAM disk

ISBN 0-9744486-5-6  

Donald K. Burleson & Mike Ault

http://www.rampant-books.com/book_2005_1_ssd.htm

  
 

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