RAID Performance
Submitted by Alexander Podelko on Thu, 24/05/2007 - 03:16.
non-functional testing | performance testing
I was asked about using RAID 5 for a database. The question is so generic, that the answer probably doesn't depend on what database management system we talk about. To refresh my vague memories I talked to some people and did a quick Internet search and got the same answer from all sources.
Brian Peasland in The best RAID configuration for Oracle 9i wrote:
Unfortunately, RAID 5 has the worst write performance of all of these RAID levels. Write operations can be twice as slow compared to a normal file system. No write intensive files should be placed on RAID 5 volumes otherwise you database peroformance can really slow to a crawl.
If you can afford it, then RAID 0+1 is probably the "best" solution.
The same opinion you can find in Oracle Database Administration: The Essential Reference:
RAID-5 is, in fact, very powerful and inexpensive. It is also a technology to be avoided in most cases when configuring your Oracle database! This may seem a harsh statement, but the reality is that although RAID-5 provides good levels of data protection at a low monetary cost, this comes at a very high cost for disk I/O. In particular, write operations on RAID-5 arrays can be orders of magnitude slower than the same operations on a single disk.
A good alternative to the RAID-5 array is the use of RAID level 0, commonly known as disk mirroring. Although more expensive than RAID-5 (one-half of the disks are used for storing redundant data), RAID-0 provides complete data protection with no sacrifice in I/O efficiency.
The best RAID performance available today is called RAID-0+1, sometimes called RAID-10. This level of RAID combines mirrored disks (as in RAID-0) with striping of data across multiple drives, which can eliminate any delay while waiting for disk head positioning. While not available from all RAID controllers, RAID-0+1 is well worth considering.
Brian Peasland in The best RAID configuration for Oracle 9i wrote:
Unfortunately, RAID 5 has the worst write performance of all of these RAID levels. Write operations can be twice as slow compared to a normal file system. No write intensive files should be placed on RAID 5 volumes otherwise you database peroformance can really slow to a crawl.
If you can afford it, then RAID 0+1 is probably the "best" solution.
The same opinion you can find in Oracle Database Administration: The Essential Reference:
RAID-5 is, in fact, very powerful and inexpensive. It is also a technology to be avoided in most cases when configuring your Oracle database! This may seem a harsh statement, but the reality is that although RAID-5 provides good levels of data protection at a low monetary cost, this comes at a very high cost for disk I/O. In particular, write operations on RAID-5 arrays can be orders of magnitude slower than the same operations on a single disk.
A good alternative to the RAID-5 array is the use of RAID level 0, commonly known as disk mirroring. Although more expensive than RAID-5 (one-half of the disks are used for storing redundant data), RAID-0 provides complete data protection with no sacrifice in I/O efficiency.
The best RAID performance available today is called RAID-0+1, sometimes called RAID-10. This level of RAID combines mirrored disks (as in RAID-0) with striping of data across multiple drives, which can eliminate any delay while waiting for disk head positioning. While not available from all RAID controllers, RAID-0+1 is well worth considering.