I've already written about changing the I/O scheduler for hard disk under Linux and avoiding sudden outburst of disk I/O using ionice utility. I/O schedulers can have many purposes such as:
Minimize time wasted by hard disk seeks.
Prioritize a certain processes' I/O requests.
Give a share of the disk bandwidth to each running process etc
Google has sponsored Gelato@UNSW to take a close look at the disk schedulers in Linux, particularly when combined with RAID. They have now published their findings:
We benchmarked the four standard Linux disk schedulers using several different tools (see our wiki for full details) and lots of different workloads, on single SCSI and SATA disks, and on hardware and software RAID arrays from two to eight spindles (hardware raid) and up to twenty spindles (software raid), trying RAID levels 0 through 6.
We had to fix some of the benchmarking tools (the fixes are now upstream), and we developed a new one: a Markov Chain based replay tool, which allows a workload to be characterised and then a similar workload generated.
=> Selected comparisons of throughput and latency with the different Linux schedulers (via Google open source blog)
A sudden outburst of violent disk I/O activity can bring down your email or web server. Usually, a web, mysql, or mail server serving millions and millions pages (requests) per months are prone to this kind of problem. Backup activity can increase current system load too. To avoid this kind of sudden outburst problem, run your script with scheduling class and priority. Linux comes with various utilities to manage this kind of madness.
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I, for one, would like to welcome our new Mozilla Firefox overload directly from deep space ;)
V838 Monocerotis (V838 Mon) is a variable star in the constellation Monoceros about 20,000 light years from the Sun. The star experienced a major outburst in early 2002. Originally believed to be a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain, but several theories have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets.
On January 10, 2002, a previously unknown star was seen to brighten up in Monoceros, the Unicorn. Being a new variable star, it was designated V838 Monocerotis, the 838th variable star of Monoceros.
(Fig. 01: Monocerotis as Firefox logo (Image credit NASA and Wired blog)
=> Firefox Logo Spied In Deep Space (via digg)