How to Choose the Right Server?

We ran variety of tests on nine different servers to determine which H/W configuration is suitable for which application.Presented here is our advice based on their results as well as other observations.

Thursday, August 16, 2007

Workgroup servers have undergone a tremendous change in recent times with a lot of new technologies hitting the market. This has made it difficult for IT decision makers to choose the right one for their organization. The demand for servers is increasing in India by leaps and bounds, and as a result we are seeing that apart from the hardware majors, a lot of assemblers are also leaving the PC space and jumping into the server arena. This has led to a major reduction in price of branded servers.

Today we are going through a phase where processor technologies are improving continuously and as a result we can now get a powerful server in just a couple of Lakhs. And it is so powerful that if you had bought it ten years back, it would have been amongst the top 50 supercomputers in the world. Such servers take up only 2 U of a server rack. This has all been made possible because of the availability of multi-core processors. Today, if you buy a server with a dual Xeon, you get either the power of eight or four Xeon processors, depending on whether you bought a quad core or a dual core server. Such a server not only gives you commendable results in number crunching operations but also help you in consolidating your datacenter. For example, the new age processors with multi-core technology provide you with Virtualization support. This means you can dedicate a single core to a given virtualized OS (which is essentially a Server) and host 7 different server OSes on a single 2 U of a dual Quad-core server. We say 7 instead of 8, as we assume that one core would be used for the host server running the virtualization application.

You might wonder that if one is going to host 7 full-fledged servers on a single quad-core server then how much memory can it support to cope with the load of all such virtualized servers running on top of it? Well, rest assured, these servers are not only capable enough to take a huge amount of processing load but can also support RAM of different capacities, starting from 8 GB to 64 GB. This is enough to host any kind of application, including resource hungry virtualization setups.

Another happening segment related to servers is storage. This segment has essentially two concepts which are gaining importance rapidly. The first is the penetration of Serial Attached SCSI (SAS) hard-disk. Since long SCSI was the de facto standard for Server Direct Attached Storage (DAS). But, due to certain limitations such as the maximum number of disks per channel and total throughout, SAS is taking its place today. You will read more about SAS and its features, later in this article. The second concept that is gaining importance is the use of Host Bus Adapter (HBA) cards. These are the cards that connect the Host (computer) to storage over iSCSI, Fiber Channel, etc. Now let's discuss all of the above points in detail.

How much RAM?
When choosing a hardware configuration, remember that each application has a different requirement. For instance, if you plan to use your server as a Web Server with a lot of static content (such as a Web portal) or as a file or networked server, then the amount of RAM doesn't really matter much, assuming you have at least 4 GB RAM. This has become standard nowadays. We came to this conclusion after running our set of I/O, disk and Web benchmarks, on the same server, with 4 GB and 8 GB RAM. In case of Web requests, the performance was the same for both configurations, while in case of file server I/O, the performance improved by 10% with higher RAM. That's hardly an increment worth spending for extra RAM.

What matters the most in these cases are disk and network speed. Once again, while testing the servers, we noticed that when you stress a server's disk access performance over the network, then the first thing to get choked is your Gigabit Ethernet card. This results in data transfer speeds of just below 1,000 Mbps. To rectify this, we joined two Ethernet cards while running network based benchmarks. Such an arrangement gave us double the bandwidth. We've given a detailed report on how we ran the benchmarks in the “how we tested' section. So here's a tip: Before thinking of upgrading your processor or RAM for I/O intensive applications, first try teaming the free LAN cards.

Some servers came with small from HDDs (Laptop HDDs), to save on space and power consumption

Which Hard Drive?
Another important parameter for I/O intensive networked servers is hard disk performance. This is also critical for database servers. But to get optimum performance, you require a very high capacity hard disk with maximum rpm and throughput, and that too in large numbers. You can actually get better performance out of five 10,000 rpm SATA HDDs than what you can get from two 15,000 rpm SAS drives. But it depends on how much you can spend and what's more important for you. If redundancy is not important and you have three HDDs, then you can connect all of them in RAID 0 (Stripping mode) and get some really extraordinary performance.

Now, if redundancy is extremely important, which is the case with most users, you can go for RAID 5 with more hard disks (let's say 6 instead of 3) so that you can reduce the performance degradation while writing parity information, and get performance which is equivalent to having two disks in RAID 0.

This time we got all the servers with hot swappable SMPS, the max number was 3

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