How Server Performance is affected by RAID, Controller Settings, and Hard Drive Selection
Your company’s servers are the backbone of your data processing and storage capabilities. Poor server performance can reduce the productivity of all your employees; in addition, it could result in lost sales or lost opportunities to reduce expenses. Making sure your server is up to the task is a wise investment.
Server Resources and Bottlenecks
The four basic parts of a server are; processors, network connections, memory or RAM, and hard drives. Processors are rarely a performance issue. Gigabit network speed is adequate for all but the most demanding networks. RAM is cheap and once you have enough, more does not help you with better performance. Performance issues are usually due to the server’s hard drive or RAID array, which is the slowest component. An upgrade in the hard drive is usually the best way to obtain increased performance.
Size, Speed, and Cost
The size and cost of a disk are well understood and marketed; with some simple math, it is easy to calculate the price per gigabyte for storage. Over time, this price has dropped considerably, and many cost conscious business owners shop for a good deal. Speed however, is less understood, not advertised, more expensive, and harder to justify since it is difficult to get either requirements or performance values up front. The main considerations are the speed of the drive itself, the number of drives used, the type of controller, and the RAID settings.
Single Hard Drive Speed
For modern servers you will be using either Serial ATA, SATA, or Serial Attached SCSI, also referred to as SAS drives. SATA drives are cheap and large, making them an incredible bargain for bulk space requirements; unfortunately, they are also slow. The RPM speed of the hard drive directly impacts how fast data can be transferred; SATA drives tend to spin at 7,200 RPM. SAS drives cost more, but spin at 10,000 RPM or 15,000 RPM. A single SAS drive will move data about twice as fast as a SATA drive. Solid State drives are just coming onto the market; they don’t have spinning disks, have very small amounts of storage, very fast performance, and are very expensive. Drives come in either 3.5 inch or 2.5 inch sizes. The larger drives will move data much faster, but the smaller ones use a lost less power and space, so a good array can be built with fewer 3.5 inch drives, or more 2.5 inch drives. Both sizes can be good solutions.
Number of Drives
More hard drives are faster than less hard drives, provided the speed of the drive and the RAID settings are the same. This is simply because there are more drives to share the work load, so data can transfer faster. For example, a 5 disk RAID 5 set of 73GB drives holds the same amount of data as a 3 disk RAID 5 set of 146GB drives, but the 5 disk set will have almost twice the performance. Additionally, if you have databases or drive intensive services, a separate set of drives for the operating system and the database is a large benefit.
Controller Settings
Controllers have to sort out all the data on multiple disks and get it back to you quickly. Hardware RAID is the only way to go on servers. The hardware RAID card will have its own processor and cache. It will have some sort of connection to the Main Board in the server and may have its own battery. More is better for all of the above; a battery backed write cache can substantially improve performance for disk writes with relatively little cost. If you have more than a couple of drives in the array, make sure the connection to the Main Board and the controller’s processor can keep up with the drives.
RAID Types
RAID comes in different formats; we will just cover the basics. RAID 0 stripes data across 2 or more drives and is the fastest, but a drive failure will destroy your data, so it is rarely used. RAID 1 mirrors the data between two hard drives, so they both have exact copies. RAID 5 stripes data across 3 or more drives and includes a parity bit in the stripe to protect against drive failure. RAID 1+0 or RAID 10, is two mirrored RAID 0 stripes of 2 or more drives; the smallest RAID 10 setup possible requires 4 hard drives.
RAID 5 Performance
RAID 5 is the best option if you want space at the expense of performance. Calculating the parity bit required for RAID 5 is hard on the controller’s processor, and only expensive controllers are up to the task. A larger number of disks in the RAID 5 array is better for both storage and speed, so while 3 disks is the minimum, it is much better to go with 5 or 9 disks. RAID 5 tends to perform poorly when lots of small read and writes are required.
RAID 1 Performance
While considered a waste of drive space, this is the most bang for your buck for speed. Even cheap controllers can simply make 2 copies of the data quickly, and multiple read requests can happen at the same time on the different disks, since they both have complete sets of data. This works very well for lots of small random reads and writes, which is what most servers do all day. If you need more performance, add a second set of disks that only supports your database, email, or files. This way you can get full speed for the data, without demands from the operating system, swap file, or logs.
RAID 10 Performance
RAID 10 lets you get big benefits from striping data without the performance hit of calculating parity. Additionally, you also get the benefit of two exact copies for simultaneous reads, just like with RAID 1. Unfortunately, this comes at the highest cost in drives, power, and space. If you need only the best, consider RAID 10 after separating out your data to a second RAID 1 set. In practice, on the fastest high performance systems, RAID 1 is used for the operating system, and RAID 10 is used for the data.
DAS and SAN options
Additional performance is possible, but requires much better controllers and large numbers of hard drives. Direct Attached Storage and Storage Area Networks can support hundreds of drives, for incredible performance. These systems can simultaneously support SATA, SAS, and Solid State drives using multiple RAID types at the same time; so if you have different types of data, with different performance and storage requirements the device can do it all. This can be cost effective when supporting multiple servers with high uptime requirements.
Summary
Your servers speed is limited by the slowest component, which is the hard drive array. If you just need lots of space with little performance, large SATA drives in a RAID 5 setup is your best bet. If you need more speed, generally upgrade in the following order:
Change to RAID 1
Use faster hard drives
Use a controller with a battery backed write cache
Separate your data onto a second RAID 1 or 5 disk RAID 5
Separate your data onto a second RAID 10
Consider Solid State, DAS, or SAN technologies
For additional information or support please contact us at 303-482-1242.
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