Pros and cons of a Journaled file System Post: 302593872

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Top Forums UNIX for Advanced & Expert Users Pros and cons of a Journaled file System Post 302593872 by methyl on Sunday 29th of January 2012 04:58:57 PM

01-29-2012

Registered User

To my surprise the Wikipedia on this subject is fairly poor (at the time of writing).
Journaling file system - Wikipedia, the free encyclopedia
As is the entry on Veritas (a popular commercial implementation).
Veritas File System - Wikipedia, the free encyclopedia

Hard discs fail. Mains power fails. Any commercial system designer must take this into account. You must always be in a position to recover from a hard disc failure or a mains power failure. Offsite backups cover you for major disaster (fire, flood etc.) but day-to-day disc failure should not interrupt processing and even a mains power failure should not corrupt your discs.

To cover this eventuality you need a Journalling Filesystem and sufficient RAID or Mirror (or preferably both) disc arrays to cover you against failure.
A half-decent Journalling Filesystem (like Veritas) tries to always maintains the visible (to software) discs in a valid state. This does not mean that you might not have to restore a backup, but that you will not have to rebuild the computer after a failure.

A single disc with Journalling Filesystem comes into the "Chocolate Teapot" category. You always need your data triplicated (or better) such that the Journalling Filesystem software can determine "WHICH IS THE BAD DISC?" and request its replacement. In the ideal world you should be able to keep running 7/24 given an infallable UPS and a 100% sound policy on replacing failed hard discs.

A recent post on this forum showed that all these precautions are worthless unless you have an alert mechanism for failed hard discs and a local process for reacting to alerts such that you immediately replace failed hard discs.

Main advantage of Journalling Filesystems:
It is possible to configure the computer to survive the common occurrence of single hard disc failure. Most importantly it is possible to configure a system to determine which is the "bad disc".

Main disadvantage of Journalling Filesystems:
Budgetary or irrational design restraints can give a wrong expectation of resilience and cause designers to be complacent about Disaster Recovery backups.

Footnote: If I have critical data on a system, the mininum disc configuration is RAID-5 Triple-mirrored. I need to be able to survive the failure of a RAID controller - not just a single disc. There are modern SANs which provide this level of hardware resilience.

Last edited by methyl; 01-29-2012 at 06:11 PM.. Reason: typos and spellin of occurrence

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intermomentary

intermomentary(6x)						XScreenSaver manual						intermomentary(6x)

NAME

       intermomentary - Visualize the momentary and aggregate intersections between slowly moving circles.

SYNOPSIS

       intermomentary  [-display  host:display.screen]	[-foreground  color]  [-background  color]  [-num-discs  disc count] [-draw-delay delayms]
       [-max-riders maxr] [-max-radius maxradius] [-fps]

DESCRIPTION

       The Intersection Momentary is a fun visualization defining the relationships between objects with Casey Reas, William Ngan, and Robert Hod-
       gin. Commissioned for display at the Whitney Museum of American Art.

       A  surface  filled with 100 medium to small sized circles. Each circle has a different size and direction, but moves at the same slow rate.
       Display:

	   A. The instantaneous intersections of the circles.
	   B. The aggregate intersections of the circles.

       The circles begin with a radius of 1 pixel and slowly increase to some arbitrary size.  Circles are drawn with small  moving  points  along
       the perimeter. The intersections are rendered as glowing orbs.  Glowing orbs are rendered only when a perimeter point moves past the inter-
       section point.

       Ported to XScreensaver from the art project "InterMomentary" at http://www.complexification.net by J.Tarbell

OPTIONS

       intermomentary accepts the following options:

       -num-discs disc count (Default: 85)
	       Number of slowly moving and growing discs to use.  The more discs, the more CPU power.

       -draw-delay delayms (Default: 30000)
	       Delay in ms between drawing cycles.  More delay, slower (but smoother and less CPU intensive.)  art.

       -max-riders maxrider (Default: 40)
	       Maximum number of 'riders', single dots moving around the edge of the discs.

       -max-radius maxradius (Default: 100)
	       Maximum possible radius of a disc.

       -fps    Display the current frame rate and CPU load.

ENVIRONMENT

       DISPLAY to get the default host and display number.

       XENVIRONMENT
	       to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.

       BUGS

       Setting the background to anything besides black confuses the intensity
	       algorithm and will look terrible.

SEE ALSO

       X(1), xscreensaver(1)

COPYRIGHT

       Copyright (C) 2003 by J. Tarbell (complex@complexification.net, http://www.complexification.net).

       Ported to XScreensaver 2004 by Mike Kershaw (dragorn@kismetwireless.net)

AUTHOR

       J. Tarbell <complex@complexification.net>, Jun-03

       Mike Kershaw <dragorn@kismetwireless.net>, Oct-04

X Version 11							5.15 (28-Sep-2011)						intermomentary(6x)