The NetBoot service, and network-based system deployment in general, is among the most demanding services you can subject your network and servers to. Therefore, before setting up your NetBoot server, you should consider the configuration factors that will affect the overall performance of your NetBoot service.
There are no theoretical client limits for the NetBoot service at this time. Rather, NetBoot performance, and thus useful client capacity, is based on network speed and server configuration. Obviously, the more clients you intend to simultaneously use the NetBoot service, the more resources you will need to devote to hosting NetBoot services. An “underpowered” NetBoot deployment will at best yield consistently poor performance and at worst simply not work at all.
Optimizing Network Performance
Though the NetBoot service supports 100Base-T Ethernet connections for the client computers, an entirely Gigabit Ethernet network should be used for all NetBoot server connections for the best performance.
Apple Xserve, PowerMac, and Mac Pro computers all support multiple Ethernet connections either built in or via additional Ethernet adapters. Thus, to enhance NetBoot service performance, you could attach each Ethernet port on your NetBoot server to separate subnets on your network.
Or if you want to use only a single IP address for your NetBoot server, Mac OS X Server v10.5 supports bonded Ethernet connections using IEEE 802.3ad link aggregation. This setup also requires network switches that support the IEEE 802.3ad standard, but it enables you to effectively multiply the bandwidth of your NetBoot server while maintaining a single IP address.
Optimizing Server Performance
For the best NetBoot performance, you should avoid running other nonrelated services on your NetBoot servers so the NetBoot service won’t have to contend with other services sapping resources from your server.
Additionally, the two factors that most affect the NetBoot performance, from a server hardware perspective, are amount of RAM and hard drive performance. The NetBoot service will cache as much of the NetBoot image in system memory as possible, so the more RAM youinstall in your server, the better.
Further, the hard drives containing the NetBoot images can be a limiting server hardware factor, so the faster the speed of the drive, the better. You can also spread the NetBoot workload across multiple drives; for instance, you can use a RAID array to increase drive performance. A better approach, however, is to use the built-in loadbalancing features of the NetBoot service, covered in the following section.
Using Load Balancing
The NetBoot service includes two methods for load-balancing demand. The first spreads the load across multiple disk drives of a NetBoot server, and the second spreads the load across multiple NetBoot servers. Both methods can be employed to provide maximum NetBoot performance. Adding more NetBoot servers increases performance more than does adding more disk drives to a single server; however, the latter solution is much less expensive. Note P Hosting your NetBoot images on multiple partitions of a single drive does not improve, and can even reduce, performance.
The goal here with load balancing is to make your NetBoot images available from as many shared disk drives as possible. Each NetBoot image has an image ID, or index value, which client computers use to identify images hosted from NetBoot shares.
When a client lists the available NetBoot images in the Startup Disk pane of System Preferences, if multiple hosted images have the same index number, the client assumes that the images are identical and displays only one entry. During the startup process, the client will attempt to connect to the least busy NetBoot share to get the best performance.
If a NetBoot image will be hosted on only a single share, it should be assigned an index value between 1 and 4095. If a NetBoot image will be hosted on multiple shares, it should be assigned a value between 4096 and 65535. In the System Image Utility when a basic NetBoot image is created, the specific index number is chosen automatically for you.
If you will be using a large number of diskless NetBoot or NetInstall clients, your NetBoot servers will also have to deal with the additional AFP overhead required for saving the client shadow files. The easiest way to boost performance in this situation is to configure your NetBoot servers to host the client shadow files on a separate hard disk from theNetBoot images.
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