Saturday, May 9, 2015

on rtfm, from a manual reader

Sometimes you're reading and researching online and you get to a post where someone is asking something very basic, or is very misinformed, and a peanut gallery lurker will inevitably step forward and suggest that the poor sap "read the fucking manual", or rtfm.  When this happens, I cheer - manpages are the bedrock of unix; once you've consumed one, you should be 100% competent in the use of that tool.

But sometimes it doesn't work out like it should.  The ip and sudoers manpages are notorious disasters.  (At one point I remember reading an in-depth writeup about what went wrong with the creation of iproute2, but I can't find it now.  If anyone else has the link, please send it to me!)

Despite some gripes I have with the command interface - the primary operations are too dangerous, so there should be no short options - mdadm has a decent manpage.  But today I came across an insane, inscrutable gem:

These same layouts are available for RAID6.  There are also  4  layouts  that  will provide  an  intermediate stage for converting between RAID5 and RAID6.  These provide a layout which is identical to the corresponding RAID5 layout on the first N-1 devices,  and has the 'Q' syndrome (the second 'parity' block used by RAID6) on the last device.  These layouts are: left-symmetric-6, right-symmetric-6, left-asymmetric-6, right-asymmetric-6, and parity-first-6.

What is the "Q" syndrome??  What does it all mean??  Google came up empty.  The world may never know.

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