RAID – not just smoke and mirrors

My final talk at Linux.conf.au 2013 was about “md” software RAID.

Slides are here and video is here (mp4).

One take away, mainly from conversations afterwards, is that – there is a perception that – it is not that uncommon for drives to fail in a way that causes them to return the wrong data without error.  Thus using checksum per block, or 3-drive RAID1 with voting, or RAID6 with P/Q checks on every read might actually be a good idea.  It is sad that such drives are not extremely uncommon, but it seems that it might be a reality.

What does one do when one finds such a drive?  Fixing the “error” can continuing quietly seems like a mistake.  Kicking the drive from the array is probably right, but might be too harsh. Stopping all IO and waiting for operator assistance is tempting…. but crazy.

I wonder…

 

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Wiggles and Diffs at LCA

My second talk at LCA2013 – the first one accepted – was on “wiggle”, my tool for applying patches that don’t apply.  In the presentation I wanted to explain how “diff” works – as I then wanted to explain why one of the things that wiggle does is more complex that a simple  “diff”.  For this I came up with a simple animation that I presented as a series of “impress” slides.  Some suggested I make them into an animated “gif”, so I did.  And here it is (click for a higher-res version):

 

 

 

Animation of Diff algorithm

See slides for explanation

 

 

 

Among the useful feedback I got about wiggle:

  • UTF-8 support would be good.  This  only applies to the way it breaks strings into words.  Currently it only understand ASCII
  • Detecting patterns of “replace A with B” and looking for unreplaced copies of “A” in the original might be useful.

The slides in LibreOffice format are here and the recording of the talk is here

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Linux.conf.au – one down, two to go.

At linux.conf.au this week and as always it is proving to be a great conference. Bdale’s keynote on Monday was a really good opening keynote: very wide-ranging, very high level, very interesting and relevant, very pragmatic and  sensible.

One of this key points was that we should all just keep building the tools we want to use and making it easy for others to contribute.  The long tail of developers who submit just one patch to the Linux kernel make a significant contribution but wouldn’t be there if it was hard to contribute, hard to get the source, or hard to build the source.  With Linux all of these are relatively easy and other projects could learn from that … particularly the “easy to build” bit.

So let’s not worry about beating MS or Apple, or about claiming the year of the Linux anything.  Let’s just do stuff we enjoy and make stuff we use and share our enthusiasm with others.  If that doesn’t lead to world domination, nothing will.

For myself, I managed to get 3 speaking slots this year … makes up for not speaking for some years I guess.  My first was yesterday about the OpenPhoenux project – follow-on from OpenMoko.  It was very well attended, I got really good responses and positive  feedback.  I even managed to finish very very nearly on time.  So overall, quite a success.  I hope the next two (both tomorrow, Wednesday)  go as well.

You can view the  slides if you like, but they aren’t as good without all the talking.  Hopefully the LCA organisers will upload the video at some stage.

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Writing for LWN

I like to write articles for LWN.net from time to time. Recently I wrong about the recently announced “f2fs” file system (https://lwn.net/Articles/518988/) and might follow it up with a couple more reviews of other filesystems.
One challenge is thinking of – or finding – interesting things to write about. I’m not expecting my loyal readership to do my work for me and provide topics, and any suggestions about general areas of interest that might spark some idea for me would not be unwelcome….

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A new blog…

I’m moving my neil.brown.name site to a new home (off in the cloud with better network connectivity – thanks Orion) and so thought it was probably time to try out different blog software.

Previously I have been using a python script I hacked up myself based on something someone else had done.  That was fun and a good start to learning python, but the functionality was always minimal and while I often put up with minimal functionality in exchange for having built it myself there comes a point where I want to move on.

This time that point was comment spam.  You would think that having a one-of-a-kind blog with a posting mechanism which is unique in details (though obviously not in principle) would make the cost of building a spam bot to post comments would just not be worth the gain.  But it seems not.  Someone did start posting comment spam – not even interesting spam for the most part, just pointless junk.  Maybe it wasn’t even someone, may it was an AI bot which worked out how to post noise all by itself.  Though when I deleted all the posts it didn’t come back for a while, so that seems to suggest a human agent.

Anyway the span has been annoying and I thought about writing some sort of protection (probably simplistic registration where I have to approve the first post by each new registrant – I don’t get so many comments that that would be a problem).  But time is short and task lists are long so it never happened.

So as I’m setting up a new server I decided to try something new and took the safe option – wordpress.  It certainly seems to be widely used and actively developed, so it must be worth a try.  I don’t even know what it does to prevent comment spam. I suspect I’ll find out once I get spam and start looking into it – but I’m sure there must be something there.

Meanwhile I and my commenters will benefit from not having to use an obscure markup language and  can just focus on generating content.

Creating the blog with wordpress meant that I needed to give my blog a cute name, so after  about 2 seconds thought I chose “A Taciturn Disposition”.  This comes from Jane Austin’s “Pride and Prejudice”.

“Are you consulting your own feelings in the present case, or do you imagine that you are gratifying mine?”

“Both,” replied Elizabeth archly; “for I have always  seen a great similarity in the turn of our minds.  We  are each of an unsocial, taciturn disposition, unwilling to speak, unless we expect to say something that will amaze the whole room, and be handed down to posterity with all the eclat of a proverb.”

I’m not really sure if Lizzie Bennet is intending this epithet as a compliment or insult, and probably means both.  But it one that I would feel comfortable with.  I’m not much good at small talk but prefer talking about issues of substance.  Certainly I wouldn’t include topics if only passing interest in a blog – that stuff, if written at all, belongs on facebook or G+.  Blogs are fore more amazing and  proverbial expositions, such as this one.

But anyway, here begins the new blog.  The old can still be found at http://neil.brown.name/blog/, while this one is http://blog.neil.brown.name/.

 

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