Systems Administration

What is RAID 0? — RAID striping explained

RAID – or “Redundant Array of Independent Disks” – is a strategy for data storage used on most server setups. Understanding how RAID works, how it can help you meet the needs of your business or organization, and understanding differences between RAID levels is important before setting up your server. This article discusses RAID 0

What is RAID 5 — RAID parity explained

It’s hard to talk about servers without RAID coming up. If you’re considering RAID for your server and want to know if RAID 5 is right for you, or if you just want to learn more about RAID in general, you’ve come to the right place. We’ll go over that and more in this article.

What is RAID 10 — Nested RAID levels explained

RAID is a topic that comes up a lot when discussing servers. If you’ve wondered what RAID is, why you might want it on your server, and whether RAID 10 is the best option for you, look no further. We’re going to be discussing all of that in today’s article. What is RAID? RAID, or

Adding AHCI support to CentOS after it was already installed in IDE mode

Sometimes when you’re using a server, you’ll notice that the disk i/o is slower than it ought to be, or is using a lot more cpu than it should be during disk i/o. In some cases, this would be because the BIOS is configured to use your sata drives in legacy IDE mode instead of

Setting up Software RAID / MDADM status alert Emails for failed drives in Centos, Ubuntu, and Debian

Issues regarding software and hardware raid are no stranger to the IOFlood blog, with articles discussing the relative merits of each, articles discussing why raid is important (and so are backups), and so on. But RAID only provides protection against failed drives if you realize a drive has failed and replace it. Often times, a

How to set up source nat routing (SNAT) in iptables to load balance outbound connections across multiple IP addresses

In our earlier days, before IOFlood, some of us ran web based proxy services. These were popular at workplaces or schools for accessing websites that were blocked there, such as gmail and myspace (remember myspace?). One common problem that came up, was that with so many users each sharing one IP on one server, our

Making sense of Linux memory usage, Part 1: how to read “top” in CentOS.

We get this question a lot, about “Why is my Linux server using so much ram?”. In many cases, it really isn’t using much ram at all, but just to be sure we always have to check. At least half the time, really very little is being used, but the way that Linux reports ram

Configuring additional IP addresses (virtual interfaces) on Centos Servers

You may have a Centos dedicated server or VPS, and you’ve been assigned additional IP addresses, which have not been configured by your hosting provider. There are good reasons your host won’t have configured these for you, because if you are using virtualization, many VPS control panels need to manage these IPs, and so it

Installing Centos 6.x onto a dedicated server with hard drives bigger than 2tb (3tb, 4tb, 6tb, 8tb, or bigger)

I’m a big fan of Centos, but like anything, it’s not perfect. In Centos 5, it is nearly impossible to get a working install onto drives larger than 2tb. In Centos 6, it is possible, but not entirely straightforward. The reason for the difficulty, is that MBR (master boot record) was designed only to support

nf_conntrack: table full, dropping packet — A solution for CentOS Dedicated Servers

A common problem you may experience is sluggish performance or disconnections from your Centos dedicated server, even though there is sufficient CPU, ram, disk i/o, etc. After some troubleshooting, you may come to believe you are being DDoS attacked, but you don’t see an unusual amount of traffic, and there’s no single IP or handful