Choosing hardware for Swift Nodes

Chris Nelson -

Although Swift runs on commodity hardware but here a couple points that need to be taken into consideration when purchasing hardware for your SwiftStack cluster: 

CPU

OpenStack Swift relies on a 64-bit x86 architecture and is designed for commodity hardware.

In general, it is best to use fairly powerful CPUs, especially if they are going to be handling proxy requests. Generally, CPU power primarily matters in the proxy, but also in cases where object nodes are very densely populated with many disks. 

Memory

In addition to supporting the Swift processes, system RAM caches the XFS inodes and works as a buffer cache to quickly serve frequently accessed objects. In general, we would suggest at least 1 GB of RAM per drive. However, just like with everything else, the amount of RAM you need depends on your needs and the configuration of other hardware. The size of hard drives and the average size of objects stored dictates the amount of RAM you need. Being able to hold all inodes in RAM would provide ultimate performance. However, in most cases that’s not necessary and would be cost prohibitive, as you could end up needing very large amounts of RAM.  

Hard Drives

All nodes require a drive for the operating system. It is common to see a pair of drives deployed using RAID1 for the operating system (OS) in order to prevent a single drive failure from taking out an entire node. This is typically the only time you’ll use RAID in a Swift node. Still, in large-scale clusters with many, many nodes, where every penny is counted to optimize for cost, it’s not uncommon to see the operating system put on a single disk, with no redundancy. After all, if you have hundreds of nodes and you lose one node for some time, you’ve only lost a percent or a fraction of a percent of your capacity. Depending on your sensitivity to failures, which should be tightly coupled with the size of your cluster, you can use desktop- or enterprise-grade drives for the OS disk. The OS doesn’t take much space, so you can use the smallest drive you can get. If using regular hard disks for the OS, it’s typically hard to find disks smaller than 250 GB. Sometimes it can be more cost effective to buy a small SSD, which many times can also be less failure prone than a regular hard drive.

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