RAID Levels and SQL Server
RAID (redundant array of independent disks) levels 0, 1, and 5 are typically implemented with SQL Server.
Level 0
This level is also known as disk striping because it uses a disk file system called a stripe set. Data is divided into blocks and spread in a fixed order among all disks in an array. RAID 0 improves read and write performance by spreading operations across multiple disks. Operations can then be performed independently and at the same time.
RAID 0 is similar to RAID 5, but RAID 5 also provides fault tolerance.
Level 1
This level is also known as disk mirroring because it uses a disk file system called a mirror set. Disk mirroring provides a redundant, identical copy of a selected disk. All data written to the primary disk is written to the mirror disk. RAID 1 provides fault tolerance and generally improves read performance but may degrade write performance.
Level 2
This level adds redundancy by using an error correction method that spreads parity across all disks. RAID 2 also uses a disk-striping strategy that divides a file into bytes and spreads it across multiple disks. This strategy offers only marginal improvement in disk use and read-and-write performance over mirroring (RAID 1). RAID 2 is not as efficient as other RAID levels and is not generally used.
Level 4
This level uses striped data in much larger blocks or segments than RAID 2 or RAID 3. Like RAID 3, the error correction method requires only one disk for parity data. This feature keeps user data separate from error-correction data. RAID 4 is not as efficient as other RAID levels and is not generally used.
Level 5
Also known as striping with parity, this level is the most popular strategy for new designs. RAID 5 is similar to RAID 4, because this level stripes the data in large blocks across the disks in an array. However, RAID 5 differs because it writes the parity across all the disks. Data redundancy is provided by the parity information. The data and parity information are arranged on the disk array so that the two types of information are always on different disks. Striping with parity offers better performance than disk mirroring (RAID 1). However, when a stripe member is missing, read performance is decreased, for example, when a disk fails.
Level 10 (1+0)
This level is also known as mirroring with striping. RAID 10 uses a striped array of disks that are then mirrored to another identical set of striped disks. For example, a striped array can be created by using five disks. The striped array of disks is then mirrored using another set of five striped disks. RAID 10 provides the performance benefits of disk striping with the disk redundancy of mirroring. RAID 10 provides the highest read-and-write performance of any one of the other RAID levels, but at the expense of using two times as many disks.
RAID levels higher than 10 (1 + 0) may offer additional fault tolerance or performance enhancements. These levels generally are proprietary systems. For more information about these types of RAID systems, contact the hardware vendor.
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Community Additions
ADDEven hardware vendors get it wrong
Cant tell you how many times I tried to purchase RAID 0+1 controllers only to find out it was actually a RAID 1+0. Now it seems MS can't get it right.
4/23/2015
Incorrect RAID 10 Description
The description of RAID 10 (1+0) in this article is incorrect. Raid 1+0 is sets of mirrored disks that are striped together, not sets of striped disks that are mirrored together (that would be RAID 0+1 instead of 1+0, sometimes also called RAID 10).
Just think of the order you have to perform the array configuration in: for 1+0, you mirror (RAID 1) the disks together, then span (RAID 0) across the RAID 1 arrays. 0+1 has you spanning (RAID 0) the sets of disks first, then mirroring (RAID 1) them together.
Just think of the order you have to perform the array configuration in: for 1+0, you mirror (RAID 1) the disks together, then span (RAID 0) across the RAID 1 arrays. 0+1 has you spanning (RAID 0) the sets of disks first, then mirroring (RAID 1) them together.
11/20/2011
SQL SERVER
The
timing of this article is both funny, and informative. I am literally
in the process right now of finishing up the design of a new database
for my company. We went with similar hardware to a previously
configuration of theirs (Dell PowerEdge R710). I beefed it out to spec
on the 6-drive bay version (wasn't bad given that there wasn't suppose
to be a budget for this project). I loaded it with 6-146gb drives, RAID
5 with a 12mb cache controller, and 8gb of RAM (wanted to start with
16, but cut it back due to going with only the 6-bay drive config).
Now
- I had not even heard of this kind of venomous talk about RAID 5 and
Databases before. My background has been in I.T. for over 10 years, and
RAID 5 was always a very popular and steady platform, for the most
part. I'm only newly born to SQL Server (since about 2004 as more of an
application analyst), and this is my first titled role as a DBA, but I
have to tell you - I would not have gone above RAID 5 for many reasons
(not the least of which is the trade off of disk space and the cost for
it), but to know that there was all this disparity (no pun intended)
over the manner in which the controller writes to the disk is nearly
laughable if not questionable. I have never heard of such things being
that bad in the past, but then again - I wasn't big on Oracle!
I'll let you know how my first endeavor goes. It's an OLTP system that is being readied for role out next week!
Best wishes to you, and keep the articles coming!
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