Книга: Windows Server 2012 R2 Storage, Security, & Networking Pocket Consultant
Improving performance and fault tolerance with RAID
Improving performance and fault tolerance with RAID
You’ll often want to give important data increased protection from drive failures. To do this, you can use RAID technology to add fault tolerance to your file systems. With RAID, you increase data integrity and availability by creating redundant copies of the data. You can also use RAID to improve your disks’ performance.
Different implementations of RAID technology are available, and these implementations are described in terms of levels. Each RAID level offers different features.
Windows Server 2012 R2 supports RAID levels 0, 1, and 5. You can use RAID-0 to improve the performance of your drives, and you use RAID-1 and RAID-5 to provide fault tolerance for data.
Table 2–2 provides a brief overview of the supported RAID levels. This support is completely software-based.
The most common RAID levels in use on servers running Windows Server 2012 R2 are level 1 (disk mirroring), and level 5 (disk striping with parity). With respect to upfront costs, disk mirroring is the least expensive way to increase data protection with redundancy. Here, you use two identically sized volumes on two different drives to create a redundant data set. If one of the drives fails, you can still obtain the data from the other drive.
However, disk striping with parity requires more disks — a minimum of three — but offers fault tolerance with less overhead than disk mirroring. If any of the drives fail, you can recover the data by combining blocks of data on the remaining disks with a parity record. Parity is a method of error checking that uses an exclusive OR operation to create a checksum for each block of data written to the disk. This checksum is used to recover data in case of failure.
TABLE 2–2 Windows Server 2012 R2 support for RAID
| RAID LEVEL | RAID TYPE | DESCRIPTION | MAJOR ADVANTAGES |
|---|---|---|---|
| 0 | Disk striping | Add the disks that contain the rest of the spanned volumes, and then import all the disks at one time. | Speed and performance. |
| 1 | Disk mirroring | Two volumes on two drives are configured identically. Data is written to both drives. If one drive fails, no data loss occurs because the other drive contains the data. (This level doesn’t include disk striping.) | Redundancy. Better write performance than disk striping with parity. |
| 5 | Disk striping with parity | Uses three or more volumes, each on a separate drive, to create a striped set with parity error checking. In the case of failure, data can be recovered. | Fault tolerance with less overhead than mirroring. Better read performance than disk mirroring. |
REAL WORLD Although it’s true that the upfront costs for mirroring should be less than the upfront costs for disk striping with parity, the actual cost per gigabyte might be higher with disk mirroring. With disk mirroring, you have an overhead of 50 percent. For example, if you mirror two 750-gigabyte (GB) drives (a total storage space of 1500 GB), the usable space is only 750 GB. With disk striping with parity, on though, you have an overhead of around 33 percent. For example, if you create a RAID-5 set by using three 500-GB drives (a total storage space of 1500 GB), the usable space (with one-third lost for overhead) is 1,000 GB.
Оглавление книги
- Разработка приложений баз данных InterBase на Borland Delphi
- Open Source Insight and Discussion
- Introduction to Microprocessors and Microcontrollers
- Chapter 6. Traversing of tables and chains
- Chapter 8. Saving and restoring large rule-sets
- Chapter 11. Iptables targets and jumps
- Chapter 5 Installing and Configuring VirtualCenter 2.0
- Chapter 16. Commercial products based on Linux, iptables and netfilter
- Appendix A. Detailed explanations of special commands
- Appendix B. Common problems and questions
- Appendix E. Other resources and links
- IP filtering terms and expressions