Deploying Suse Linux Enterprise Server
 |
Purchase "Deploying Suse Linux Enterprise Server" at Lulu.com |
Installing Suse Linux Enterprise Server
RAID Arrays
The first part of the disk subsystem that we will look at is implementing some sort of RAID (Redundant Array of Inexpensive Disks) Array, instead of using single disk drives. In a nutshell, a RAID array spreads data across two or more physical disk drives. This gives many benefits such as:
- Increased storage space by having a storage system that can be much larger that what a single hard disk drive can provide
- Increased speed by reading data from multiple disks
- Data redundancy by configuring the RAID array to write the same data to multiple disks to reduce the risk of data loss if one drive stops working
RAID Arrays can be configured in various ways, these are referred to as RAID Levels. The most useful RAID levels in use are RAID Level 0, 1 and 5.
RAID 0 - With this RAID Level, the member drive's capacities are all added together to create a large storage space. The read and write speeds are increased since the data is read from and written across multiple drives, but there is no redundancy to this RAID level. If one of the drives fails, the data is lost.
RAID 1 - This RAID level is also known as "disk mirroring". The data is "mirrored" on two or more drives in this array. This RAID level provides fault tolerance, but only allows for the storage space of the smallest drive in the array. Read speed can be greatly increased with this RAID level, but write speed (at best) is only as good as the write speed of a single drive.
With RAID 1, you can add a spare drive that will act as what is called a "Hot Spare", which will be enabled only when another drive in the array fails.
RAID 5 - This RAID level is probably the most used. Here you have three or more drives that act similarly to RAID level 0, except that additional "parity information" is written across the drives, thus if one drive fails the data is not lost. In addition to providing Fault Tolerance, both read and write performance usually increase. The storage size of a RAID 5 array increases with the number of drives added ( Number of drives - 1 * storage size of the drives).
With RAID 5, you can also add a spare drive that will act as what is called a "Hot Spare", which will be enabled only when another drive in the array fails.
Along with these RAID levels, you can actually "combine" different RAID levels to suit your needs. For instance RAID 1+0 (sometimes referred to RAID 10) combines two RAID 1 arrays into a larger RAID 0 array. This way utilizes the fault tolerance feature of RAID 1, but still gain the benefits of RAID 0 (increased performance and storage). Similarly, RAID 5+0 (or RAID 50) combines the features of RAID 5 with RAID 0.
Hardware vs Software RAID
Along with deciding which RAID level to deploy on your servers, you also have the decision on whether or not to use a Hardware based RAID solution or use the Software RAID solution that is available on Suse Linux Enterprise Server. This decision is hardly ever cut and dry, both solutions have their benefits and shortcomings, and neither solution is the best at every situation.
With that said, there is usually one situation that a Hardware RAID Solution will always be better than a software RAID solution, and that is if you are going to implement a RAID level 1 (mirroring) solution. This is due to the fact that a software RAID solution will have to write the data to multiple drives, which could saturate the bus. With a hardware solution, your data only has to go across the bus once and the controller takes care of writing the redundant data to every drive in the array.
However, there is one thing I want to stress here: Not all "RAID Adapters" are true "Hardware RAID Solutions". A "Hardware RAID controller" is an adapter that has the "electronics" on-board that takes care of handling the processing of the RAID Array. Usually these controllers also have separate cache memory and some even have a power backup device (such as a battery) to ensure data that has not been written to the disks survives a power failure.
Unfortunately, most RAID controllers available today do not have the electronics to handle the processing of the RAID array. Instead they rely on software stored in it's BIOS, or even within the it's "Device Drivers" for it's RAID functionality. These controllers offer no real benefit over the software RAID available with Suse Linux Enterprise, and most will actually perform worse. Also, many of the companies that create these devices do not create GNU/Linux device drivers, or if they do, they are usually distributed as binaries that are usually not updated regularly - this results in your in-ability to update or create a custom built Linux Kernel for your server.
|
Purchase "Deploying Suse Linux Enterprise Server" at Lulu.com |
