Disk Performance, Part 2: RAID Layouts and Stripe Sizing

In Part 1, I discussed how storage performance is typically measured in random IOPS, and talked about how to calculate them for a single spinning disk and a RAID array. Today, I’m going to get into the nitty-gritty of striping in RAID-5 and RAID-6, and discuss how to determine the optimal stripe width for your server configuration. For a lot of workloads, this will be premature optimization. I’d advise you not to think too hard about your storage subsystem unless you’re actually worried that you will be I/O-constrained. Most of these considerations, implemented appropriately, will cut down on your total … Continue Reading →

Disk Performance, Part 1: How Performance Is Measured

When we as computer users think of disk performance, we usually think about streaming, sequential performance, otherwise known as throughput. Desktop operating systems have trained us to think in this way, because the most prominent display of disk speed that your average person sees is an Explorer or Finder window showing file copy progress — we know that our music collection is being copied at 25 MB per second, for example. This measurement is a good fit for the task, because it gives us the best approximation of how long it will take until the file copy is finished. In … Continue Reading →

Runbooks are stupid and you’re doing them wrong

Well, maybe you are and maybe you aren’t. I have no idea. But if your shop is anything like the majority of IT shops I’ve seen, then this assessment is probably on the money. The runbook is one of the most pervasively mediocre, poorly thought-out and badly-implemented concepts in the entire IT industry. For those of you who are unfamiliar with the term, the runbook is basically a “how can grandma run this application?” document. Their use should be very strongly scrutinized.