RAID Level | Format | Number of Disks | Array Size | Description |
0 | Striping | 2 or more | 80GB * # of disks used | Technically not a RAID type because it provides no redundancy, RAID 0 arrays stripe the data written to the array equally across each disk in the array. This results in an increase in disk read/write performance, but if one of the devices in the array fails, the entire array fails. |
1 | Mirroring | 2 | 80GB | RAID 1 arrays are disk mirrors. The data written to one disk is also written to the other. There is no read/write performance gain in a RAID 1 array, but if one of the devices fails, the other device kicks in, and no data is lost. |
5 | Striping with Parity | 3 or more | 160GB with three disks, 240GB with four disks, 320GB with five ((n-1)*# of disks) | RAID 5 arrays combine fault tolerance with improved read/write performance. When data is written to a RAID 5 array, a portion of the data is written to all but one member of the array. Parity information is written to the remaining member. If one member of the array fails, the remaining members have sufficient information to rebuild data on the array when read. RAID 5 is more efficient with disk space than RAID 1 but can cost more because more disks are needed than in a RAID 1 array. |
6 | Striping with Dual Parity | 4 or more | 160GB with four disks, 240GB with five disks, 320GB with six ((n-2)*# of disks) | RAID 6 arrays combine fault tolerance similar to RAID 5, but has enhanced performance in that a RAID 6 array can handle the loss of two members of the array and continue functioning. Two sets of parity information are written to the disks in addition to the data. RAID 6 makes sense for larger element arrays where the chance of individual element failure is increased. Performance during failure and rebuild with RAID 6 is significantly slower because the controller has to perform two parity calculations. |
10 (a.k.a. 1+0) | Striping with mirroring | 4 or more (in multiples of 2) | 160GB with four disks, 240GB with six disks, 320GB with eight disks | RAID 10 is really a RAID 0 (striped) array made up of RAID 1 (mirrored) elements. Two pairs of mirrored disks are connected, and data is striped across the pairs. Offers some read/write performance improvement over a RAID 1 array and adds fault tolerance to a RAID 0 array. There is a greater amount of overhead in processing this type of array and is costlier to implement because a minimum of four disks are needed. One element in each mirror can be lost with no data loss, but fault tolerance is effectively lost across the entire array with the loss of only one disk. |
50 (a.k.a. 5+0) | Striping with parity sets | 6 or more | 320GB with six disks, 480GB with eight disks | RAID 50 is really a RAID 0 (striped) array made up of RAID 5 (parity) elements. Two or more sets of RAID 5 arrays are set up in a striped configuration. This configuration offers better read/write performance than RAID 10, but is much costlier in terms of disks needed at a minimum and the controller to manage the array. One element in each parity set can be lost with no loss of data, but fault tolerance is effectively lost across the entire array with the loss of only one disk. |
Backup Technologies
One of the most significant changes to backup in SBS 2008 actually comes from a change in Server 2008—no tape drive support in the native backup tools. The backup tools in Server 2008 make use of an imaging technology that writes backup data to hard disk rather than tape, and SBS 2008 inherits that change. Now, this does not mean that you cannot use a tape drive to do backups in SBS 2008; it simply means that the native tools will not write to the tape drive. If you want to use tape technology, you need to use a third-party solution for that.
Making the correct decision about which backup technology to use is important during the planning stage. External USB storage drives have become popular in the last few years, but those devices are far from the only option when looking into SBS 2008. Most name-brand OEM server manufacturers include multiple USB ports on their server configurations, but a few are beginning to include other ports on the server as well. Some servers can be configured with a Firewire (IEEE1394) interface, and others have started including eSATA connectors. Although each of these technologies has their own individual advantages when compared with the others, they all have a similar challenge when dealing with SBS 2008—how to safely disconnect the external drive from the server to rotate the backup media.
In addition, you need to have an external backup disk that is at least as large as the combined capacity available on the server to successfully back up the server. If there is going to be a large amount of data churn on the system, you may want to look at backup devices that have double or triple the capacity of the internal storage to ensure that there is room for incremental backup files during the backup process.
For a complete discussion about backup technologies and how to use the native tools, see Chapter 17, "Managing Server and Workstation Security," and Chapter 18, "Backup and Disaster Recovery."
Summary
Now that you've looked at all the options you need to consider for the design of the server and the network, you should be ready to prepare a proposal that outlines how the installation should look. Be sure to include the technical as well as the business justifications for the choices made in the proposal.
Best Practice Summary
Determining the Number and Type of CALs Needed—Purchase a sufficient number of User CALs to cover all the employees in the organization. Only look at Device CALs in a shift-work environment where employees are sharing terminals.
Selecting the Internal Network Address Range—The internal address range for the SBS 2008 network should not be one of the commonly-used address ranges used by routers and firewalls (that is, 192.168.0.x, 192.168.1.x). The internal address should be unique so users and support staff can make incoming VPN connections, if needed.
Use SBS as the DHCP Server for the Network—To ensure that workstations and other network devices have the correct settings to allow them to communicate efficiently with the SBS server, use the DHCP services on the SBS server instead of the DHCP services on the firewall or other device.
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