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Links September 2014

Matt Palmer wrote a short but informative post about enabling DNS in a zone [1]. I really should setup DNSSEC on my own zones.

Paul Wayper has some insightful comments about the Liberal party’s nasty policies towards the unemployed [2]. We really need a Basic Income in Australia.

Joseph Heath wrote an interesting and insightful article about the decline of the democratic process [3]. While most of his points are really good I’m dubious of his claims about twitter. When used skillfully twitter can provide short insights into topics and teasers for linked articles.

Sarah O wrote an insightful article about NotAllMen/YesAllWomen [4]. I can’t summarise it well in a paragraph, I recommend reading it all.

Betsy Haibel wrote an informative article about harassment by proxy on the Internet [5]. Everyone should learn about this before getting involved in discussions about “controversial” issues.

George Monbiot wrote an insightful and interesting article about the referendum for Scottish independence and the failures of the media [6].

Mychal Denzel Smith wrote an insightful article “How to know that you hate women” [7].

Sam Byford wrote an informative article about Google’s plans to develop and promote cheap Android phones for developing countries [8]. That’s a good investment in future market share by Google and good for the spread of knowledge among people all around the world. I hope that this research also leads to cheap and reliable Android devices for poor people in first-world countries.

Deb Chachra wrote an insightful and disturbing article about the culture of non-consent in the IT industry [9]. This is something we need to fix.

David Hill wrote an interesting and informative article about the way that computer game journalism works and how it relates to GamerGate [10].

Anita Sarkeesian shares the most radical thing that you can do to support women online [11]. Wow, the world sucks more badly than I realised.

Michael Daly wrote an article about the latest evil from the NRA [12]. The NRA continues to demonstrate that claims about “good people with guns” are lies, the NRA are evil people with guns.

Cheap 3G Data in Australia

The Request

I was asked for advice about cheap 3G data plans. One of the people who asked me has a friend with no home Internet access, the friend wants access but doesn’t want to pay too much. I don’t know whether the person in question can’t use ADSL/Cable (maybe they are about to move house) or whether they just don’t want to pay for it.

3G data in urban areas in Australia is fast enough for most Internet use. But it’s not good for online games or VOIP. It’s also not very useful for Youtube and other online video. There is a variety of 3G speed testing apps for Android phones and there are presumably similar apps for the iPhone. Before signing up for 3G at home it’s probably best to get a friend who’s on the network in question to test Internet speed at your house, it would be annoying to sign up for an annual contract and then discover that your home is in a 3G dead spot.

Cheapest Offers

The best offer at the moment for moderate data use seems to be Amaysim with 10G for $99.90 and an expiry time of 365 days [1]. 10G in a year isn’t a lot, but it’s pre-paid so the user can buy another 10G of data whenever they want. At the moment $10 for 1G of data in a month and $20 for 2G of data in a month seem to be common offerings for 3G data in Australia. If you use exactly 1G per month then Amaysim isn’t any better than a number of other telcos, but if your usage varies (as it does with most people) then spreading the data use over several months offers significant savings without the need to save big downloads for the last day of the month.

For more serious Internet use Virgin has pre-paid offerings of 6G for $30 and 12G for $40 which has to be used in a month [2]. Anyone who uses an average of more than 3G per month will get better value from the Virgin offers.

If anyone knows of cheaper options than Amaysim and Virgin then please let me know.

Better Coverage

Both Amaysim and Virgin use the Optus network which covers urban areas quite well. I used Virgin a few years ago (and presume that it has only improved since then) and my wife uses Amaysim now. I haven’t had any great problems with either telco. If you need better coverage than the Optus network provides then Telstra is the only option. Telstra have a number of prepaid offers, the most interesting is $100 for 10G of data that expires in 90 days [3].

That Telstra offer is the same price as the Amaysim offer and only slightly more expensive than Virgin if you average 3.3G per month. It’s a really good deal if you average 3.3G per month as you can expect it to be faster and have better coverage.

Which One to Choose?

I think that the best option for someone who is initially connecting their home via 3g is to start with Amaysim. Amaysim is the cheapest for small usage and they have an Amaysim Android app and web page for tracking usage. After using a few gig of data on Amaysim it should be possible to determine which plan is going to be most economical in the long term.

Connecting to the Internet

To get the best speed you need a 4G AKA LTE connection. But given that 3G speed is great enough to use expensive amounts of data it doesn’t seem necessary to me. I’ve done a lot of work over the Internet with 3G from Virgin, Kogan, Aldi, and Telechoice and haven’t felt a need to pay for anything faster.

I think that the best thing to do is to use an old phone running Android 2.3 or iOS 4.3 as a Wifi access point. The cost of a dedicated 3G Wifi AP is enough to significantly change the economics of such Internet access and most people have access to old smart phones.

Inteltech/Clicksend SMS Script

USER=username
API_KEY=1234ABC
OUTPUTDIR=/var/spool/sms
LOG_SERVICE=local1

I’ve just written the below script to send SMS via the inteltech.com/clicksend.com service. It takes the above configuration in /etc/sms-pass.cfg where the username is assigned with the clicksend web page and the API key is a long hex string that clicksend provides as a password. The LOG_SERVICE is which syslog service to use for the log messages, on systems that are expected to send many messages I use the service “local1″ and I use “user” for development systems.

I hope this is useful to someone, and if you have any ideas for improvement then please let me know.

#!/bin/sh
# $1 is destination number
# text is on standard input
# standard output gives message ID on success, and 0 is returned
# standard error gives error from server on failure, and 1 is returned

. /etc/sms-pass.cfg
OUTPUT=$OUTPUTDIR/out.$$
TEXT=`tr "[:space:]" + | cut -c 1-159`

logger -t sms -p $LOG_SERVICE.info "sending message to $1"
wget -O $OUTPUT "https://api.clicksend.com/http/v2/send.php?method=http&username=$USER&key=$API_KEY&to=$1&message=$TEXT" > /dev/null 2> /dev/null

if [ "$?" != "0" ]; then
  echo "Error running wget" >&2
  logger -t sms -p $LOG_SERVICE.err "failed to send message \"$TEXT\" to $1 – wget error"
  exit 1
fi

if ! grep -q ^.errortext.Success $OUTPUT ; then
  cat $OUTPUT >&2
  echo >&2
  ERR=$(grep ^.errortext $OUTPUT | sed -e s/^.errortext.// -e s/..errortext.$//)
  logger -t sms -p $LOG_SERVICE.err "failed to send message \"$TEXT\" to $1 – $ERR"
  rm $OUTPUT
  exit 1
fi

ID=$(grep ^.messageid $OUTPUT | sed -e s/^.messageid.// -e s/..messageid.$//)
rm $OUTPUT

logger -t sms -p $LOG_SERVICE.info "sent message to $1 with ID $ID"
exit 0

Links August 2014

Matt Palmer wrote a good overview of DNSSEC [1].

Sociological Images has an interesting article making the case for phasing out the US $0.01 coin [2]. The Australian $0.01 and $0.02 coins were worth much more when they were phased out.

Multiplicity is a board game that’s designed to address some of the failings of SimCity type games [3]. I haven’t played it yet but the page describing it is interesting.

Carlos Buento’s article about the Mirrortocracy has some interesting insights into the flawed hiring culture of Silicon Valley [4].

Adam Bryant wrote an interesting article for NY Times about Google’s experiments with big data and hiring [5]. Among other things it seems that grades and test results have no correlation with job performance.

Jennifer Chesters from the University of Canberra wrote an insightful article about the results of Australian private schools [6]. Her research indicates that kids who go to private schools are more likely to complete year 12 and university but they don’t end up earning more.

Kiwix is an offline Wikipedia reader for Android, needs 9.5G of storage space for the database [7].

Melanie Poole wrote an informative article for Mamamia about the evil World Congress of Families and their connections to the Australian government [8].

The BBC has a great interactive web site about how big space is [9].

The Raspberry Pi Spy has an interesting article about automating Minecraft with Python [10].

Wired has an interesting article about the Bittorrent Sync platform for distributing encrypted data [11]. It’s apparently like Dropbox but encrypted and decentralised. Also it supports applications on top of it which can offer social networking functions among other things.

ABC news has an interesting article about the failure to diagnose girls with Autism [12].

The AbbottsLies.com.au site catalogs the lies of Tony Abbott [13]. There’s a lot of work in keeping up with that.

Racialicious.com has an interesting article about “Moff’s Law” about discussion of media in which someone says “why do you have to analyze it” [14].

Paul Rosenberg wrote an insightful article about conservative racism in the US, it’s a must-read [15].

Salon has an interesting and amusing article about a photography project where 100 people were tased by their loved ones [16]. Watch the videos.

Men Commenting on Women’s Issues

A lecture at LCA 2011 which included some inappropriate slides was followed by long discussions on mailing lists. In February 2011 I wrote a blog post debunking some of the bogus arguments in two lists [1]. One of the noteworthy incidents in the mailing list discussion concerned Ted Ts’o (an influential member of the Linux community) debating the definition of rape. My main point on that issue in Feb 2011 was that it’s insensitive to needlessly debate the statistics.

Recently Valerie Aurora wrote about another aspect of this on The Ada Initiative blog [2] and on her personal blog. Some of her significant points are that conference harassment doesn’t end when the conference ends (it can continue on mailing lists etc), that good people shouldn’t do nothing when bad things happen, and that free speech doesn’t mean freedom from consequences or the freedom to use private resources (such as conference mailing lists) without restriction.

Craig Sanders wrote a very misguided post about the Ted Ts’o situation [3]. One of the many things wrong with his post is his statement “I’m particularly disgusted by the men who intervene way too early – without an explicit invitation or request for help or a clear need such as an immediate threat of violence – in womens’ issues“.

I believe that as a general rule when any group of people are involved in causing a problem they should be involved in fixing it. So when we have problems that are broadly based around men treating women badly the prime responsibility should be upon men to fix them. It seems very clear that no matter what scope is chosen for fixing the problems (whether it be lobbying for new legislation, sociological research, blogging, or directly discussing issues with people to change their attitudes) women are doing considerably more than half the work. I believe that this is an indication that overall men are failing.

Asking for Help

I don’t believe that members of minority groups should have to ask for help. Asking isn’t easy, having someone spontaneously offer help because it’s the right thing to do can be a lot easier to accept psychologically than having to beg for help. There is a book named “Women Don’t Ask” which has a page on the geek feminism Wiki [4]. I think the fact that so many women relate to a book named “Women Don’t Ask” is an indication that we shouldn’t expect women to ask directly, particularly in times of stress. The Wiki page notes a criticism of the book that some specific requests are framed as “complaining”, so I think we should consider a “complaint” from a woman as a direct request to do something.

The geek feminism blog has an article titled “How To Exclude Women Without Really Trying” which covers many aspects of one incident [5]. Near the end of the article is a direct call for men to be involved in dealing with such problems. The geek feminism Wiki has a page on “Allies” which includes “Even a blog post helps” [6]. It seems clear from public web sites run by women that women really want men to be involved.

Finally when I get blog comments and private email from women who thank me for my posts I take it as an implied request to do more of the same.

One thing that we really don’t want is to have men wait and do nothing until there is an immediate threat of violence. There are two massive problems with that plan, one is that being saved from a violent situation isn’t a fun experience, the other is that an immediate threat of violence is most likely to happen when there is no-one around to intervene.

Men Don’t Listen to Women

Rebecca Solnit wrote an article about being ignored by men titled “Men Explain Things to Me” [7]. When discussing women’s issues the term “Mansplaining” is often used for that sort of thing, the geek feminism Wiki has some background [8]. It seems obvious that the men who have the greatest need to be taught some things related to women’s issues are the ones who are least likely to listen to women. This implies that other men have to teach them.

Craig says that women need “space to discover and practice their own strength and their own voices“. I think that the best way to achieve that goal is to listen when women speak. Of course that doesn’t preclude speaking as well, just listen first, listen carefully, and listen more than you speak.

Craig claims that when men like me and Matthew Garrett comment on such issues we are making “women’s spaces more comfortable, more palatable, for men“. From all the discussion on this it seems quite obvious that what would make things more comfortable for men would be for the issue to never be discussed at all. It seems to me that two of the ways of making such discussions uncomfortable for most men are to discuss sexual assault and to discuss what should be done when you have a friend who treats women in a way that you don’t like. Matthew has covered both of those so it seems that he’s doing a good job of making men uncomfortable – I think that this is a good thing, a discussion that is “comfortable and palatable” for the people in power is not going to be any good for the people who aren’t in power.

The Voting Aspect

It seems to me that when certain issues are discussed we have a social process that is some form of vote. If one person complains then they are portrayed as crazy. When other people agree with the complaint then their comments are marginalised to try and preserve the narrative of one crazy person. It seems that in the case of the discussion about Rape Apology and LCA2011 most men who comment regard it as one person (either Valeria Aurora or Matthew Garrett) causing a dispute. There is even some commentary which references my blog post about Rape Apology [9] but somehow manages to ignore me when it comes to counting more than one person agreeing with Valerie. For reference David Zanetti was the first person to use the term “apologist for rapists” in connection with the LCA 2011 discussion [10]. So we have a count of at least three men already.

These same patterns always happen so making a comment in support makes a difference. It doesn’t have to be insightful, long, or well written, merely “I agree” and a link to a web page will help. Note that a blog post is much better than a comment in this regard, comments are much like conversation while a blog post is a stronger commitment to a position.

I don’t believe that the majority is necessarily correct. But an opinion which is supported by too small a minority isn’t going to be considered much by most people.

The Cost of Commenting

The Internet is a hostile environment, when you comment on a contentious issue there will be people who demonstrate their disagreement in uncivilised and even criminal ways. S. E. Smith wrote an informative post for Tiger Beatdown about the terrorism that feminist bloggers face [11]. I believe that men face fewer threats than women when they write about such things and the threats are less credible. I don’t believe that any of the men who have threatened me have the ability to carry out their threats but I expect that many women who receive such threats will consider them to be credible.

The difference in the frequency and nature of the terrorism (and there is no other word for what S. E. Smith describes) experienced by men and women gives a vastly different cost to commenting. So when men fail to address issues related to the behavior of other men that isn’t helping women in any way. It’s imposing a significant cost on women for covering issues which could be addressed by men for minimal cost.

It’s interesting to note that there are men who consider themselves to be brave because they write things which will cause women to criticise them or even accuse them of misogyny. I think that the women who write about such issues even though they will receive threats of significant violence are the brave ones.

Not Being Patronising

Craig raises the issue of not being patronising, which is of course very important. I think that the first thing to do to avoid being perceived as patronising in a blog post is to cite adequate references. I’ve spent a lot of time reading what women have written about such issues and cited the articles that seem most useful in describing the issues. I’m sure that some women will disagree with my choice of references and some will disagree with some of my conclusions, but I think that most women will appreciate that I read what women write (it seems that most men don’t).

It seems to me that a significant part of feminism is about women not having men tell them what to do. So when men offer advice on how to go about feminist advocacy it’s likely to be taken badly. It’s not just that women don’t want advice from men, but that advice from men is usually wrong. There are patterns in communication which mean that the effective strategies for women communicating with men are different from the effective strategies for men communicating with men (see my previous section on men not listening to women). Also there’s a common trend of men offering simplistic advice on how to solve problems, one thing to keep in mind is that any problem which affects many people and is easy to solve has probably been solved a long time ago.

Often when social issues are discussed there is some background in the life experience of the people involved. For example Rookie Mag has an article about the street harassment women face which includes many disturbing anecdotes (some of which concern primary school students) [12]. Obviously anyone who has lived through that sort of thing (which means most women) will instinctively understand some issues related to threatening sexual behavior that I can’t easily understand even when I spend some time considering the matter. So there will be things which don’t immediately appear to be serious problems to me but which are interpreted very differently by women. The non-patronising approach to such things is to accept the concerns women express as legitimate, to try to understand them, and not to argue about it. For example the issue that Valerie recently raised wasn’t something that seemed significant when I first read the email in question, but I carefully considered it when I saw her posts explaining the issue and what she wrote makes sense to me.

I don’t think it’s possible for a man to make a useful comment on any issue related to the treatment of women without consulting multiple women first. I suggest a pre-requisite for any man who wants to write any sort of long article about the treatment of women is to have conversations with multiple women who have relevant knowledge. I’ve had some long discussions with more than a few women who are involved with the FOSS community. This has given me a reasonable understanding of some of the issues (I won’t claim to be any sort of expert). I think that if you just go and imagine things about a group of people who have a significantly different life-experience then you will be wrong in many ways and often offensively wrong. Just reading isn’t enough, you need to have conversations with multiple people so that they can point out the things you don’t understand.

This isn’t any sort of comprehensive list of ways to avoid being patronising, but it’s a few things which seem like common mistakes.

Anne Onne wrote a detailed post advising men who want to comment on feminist blogs etc [13], most of it applies to any situation where men comment on women’s issues.

Being Obviously Wrong About Autism

I’m watching a Louis Theroux documentary about Autism (here’s the link to the BBC web site [1]). The main thing that strikes me so far (after watching 7.5 minutes of it) is the bad design of the DLC-Warren school for Autistic kids in New Jersey [2].

A significant portion of people on the Autism Spectrum have problems with noisy environments, whether most Autistic people have problems with noise depends on what degree of discomfort is considered a problem. But I think it’s reasonable to assume that the majority of kids on the Autism Spectrum will behave better in a quiet environment. So any environment that is noisy will cause more difficult behavior in most Autistic kids and the kids who don’t have problems with the noise will have problems with the way the other kids act. Any environment that is more prone to noise pollution than is strictly necessary is hostile to most people on the Autism Spectrum and all groups of Autistic people.

The school that is featured in the start of the documentary is obviously wrong in this regard. For starters I haven’t seen any carpet anywhere. Carpeted floors are slightly more expensive than lino but the cost isn’t significant in terms of the cost of running a special school (such schools are expensive by private-school standards). But carpet makes a significant difference to ambient noise.

Most of the footage from that school included obvious echos even though they had an opportunity to film when there was the least disruption – presumably noise pollution would be a lot worse when a class finished.

It’s not difficult to install carpet in all indoor areas in a school. It’s also not difficult to install rubber floors in all outdoor areas in a school (it seems that most schools are doing this already in play areas for safety reasons). For a small amount of money spent on installing and maintaining noise absorbing floor surfaces the school could achieve better educational results. The next step would be to install noise absorbing ceiling tiles and wallpaper, that might be a little more expensive to install but it would be cheap to maintain.

I think that the hallways in a school for Autistic kids should be as quiet as the lobby of a 5 star hotel. I don’t believe that there is any technical difficulty in achieving that goal, making a school look as good as an expensive hotel would be expensive but giving it the same acoustic properties wouldn’t be difficult or expensive.

How do people even manage to be so wrong about such things? Do they never seek any advice from any adult on the Autism Spectrum about how to run their school? Do they avoid doing any of the most basic Google searches for how to create a good environment for Autistic people? Do they just not care at all and create an environment that looks good to NTs? If they are just trying to impress NTs then why don’t they have enough pride to care that people like me will know how bad they are? These aren’t just rhetorical questions, I’d like to know what’s wrong with those people that makes them do their jobs in such an amazingly bad way.

Booting GPT

I’m installing new 4TB disks on an older Dell server, it’s a PowerEdge T110 with a G6950 CPU so it’s not really old, but it’s a couple of generations behind the latest Dell servers.

I tried to enable UEFI booting, but when I turned that option on the system locked up during the BIOS process (wouldn’t boot from the CD or take keyboard input). So I had to make it boot with a BIOS compatible MBR and a GPT partition table.

Number  Start (sector)    End (sector)  Size      Code  Name
  1            2048            4095  1024.0 KiB  EF02  BIOS boot partition
  2            4096        25169919  12.0 GiB    FD00  Linux RAID
  3        25169920      7814037134  3.6 TiB    8300  Linux filesystem

After spending way to much time reading various web pages I discovered that the above partition table works. The 1MB partition is for GRUB code and needs to be enabled by a parted command such as the following:

parted /dev/sda set 1 bios_grub on

/dev/sda2 is a RAID-1 array used for the root filesystem. If I was installing a non-RAID system I’d use the same partition table but with a type of 8300 instead of FD00. I have a RAID-1 array over sda2 and sdb2 for the root filesystem and sda3, sdb3, sdc3, sdd3, and sde3 are used for a RAID-Z array. I’m reserving space for the root filesystem on all 5 disks because it seems like a good idea to use the same partition table and the 12G per disk that is unused on sdc, sdd, and sde isn’t worth worrying about when dealing with 4TB disks.

More BTRFS Fun

I wrote a BTRFS status report yesterday commenting on the uneventful use of BTRFS recently [1].

Early this morning the server that stores my email (which had 93 days uptime) had a filesystem related problem. The root filesystem became read-only and then the kernel message log filled with unrelated messages so there was no record of the problem. I’m now considering setting up rsyslogd to log the kernel messages to a tmpfs filesystem to cover such problems in future. As RAM is so cheap it wouldn’t matter if a few megs of RAM were wasted by that in normal operation if it allowed me to extract useful data when something goes really wrong. It’s really annoying to have a system in a state where I can login as root but not find out what went wrong.

After that I tried 2 kernels in the 3.14 series, both of which had kernel BUG assertions related to Xen networking and failed to network correctly, I filed Debian Bug #756714. Fortunately they at least had enough uptime for me to run a filesystem scrub which reported no errors.

Then I reverted to kernel 3.13.10 but the reboot to apply that kernel change failed. Systemd was unable to umount the root filesystem (maybe because of a problem with Xen) and then hung the system instead of rebooting, I filed Debian Bug #756725. I believe that if asked to reboot a system there is no benefit in hanging the system with no user space processes accessible. Here are some useful things that systemd could have done:

  1. Just reboot without umounting (like “reboot -nf” does).
  2. Pause for some reasonable amount of time to give the sysadmin a possibility of seeing the error and then rebooting.
  3. Go back to a regular runlevel, starting daemons like sshd.
  4. Offer a login prompt to allow the sysadmin to login as root and diagnose the problem.

Options 1, 2, and 3 would have saved me a bit of driving. Option 4 would have allowed me to at least diagnose the problem (which might be worth the drive).

Having a system on the other side of the city which has no remote console access just hang after a reboot command is not useful, it would be near the top of the list of things I don’t want to happen in that situation. The best thing I can say about systemd’s operation in this regard is that it didn’t make the server catch fire.

Now all I really know is that 3.14 kernels won’t work for my server, 3.13 will cause problems that no-one can diagnose due to lack of data, and I’m now going to wait for it to fail again. As an aside the server has ECC RAM and it’s hardware is known to be good, so I’m sure that BTRFS is at fault.

Links July 2014

Dave Johnson wrote an interesting article for Salon about companies ripping off the tax system by claiming that all their income is produced in low tax countries [1].

Seb Lee-Delisle wrote an insightful article about how to ask to get paid to speak [2]. I should do that.

Daniel Pocock wrote an informative article about the reConServer simple SIP conferencing server [3]. I should try it out, currently most people I want to conference with are using Google Hangouts, but getting away from Google is a good thing.

François Marier wrote an informative post about hardening ssh servers [4].

S. E. Smith wrote an interesting article “I Am Tired of Hearing Programmers Defend Gender Essentialism [5].

Bert Archer wrote an insightful article about lazy tourism [6]. His initial example of “love locks” breaking bridges was a bit silly (it’s not difficult to cut locks off a bridge) but his general point about lazy/stupid tourism is good.

Daniel Pocock wrote an insightful post about new developments in taxis, the London Taxi protest against Uber, and related changes [7]. His post convinced me that Uber is a good thing and should be supported. I checked the prices and unfortunately Uber is more expensive than normal taxis for my most common journey.

Cory Doctorow wrote an insightful article for The Guardian about the moral issues related to government spying [8].

The Verge has an interesting review of the latest Lytro Lightbox camera [9]. Not nearly ready for me to use, but interesting technology.

Prospect has an informative article by Kathryn Joyce about the Protestant child sex abuse scandal in the US [10]. Billy Graham’s grandson is leading the work to reform churches so that they protect children instead of pedophiles. Prospect also has an article by Kathryn Joyce about Christians home-schooling kids to try and program them to be zealots and how that hurts kids [11].

The Daily Beast has an interesting article about the way that the extreme right wing in the US are trying to kill people, it’s the right wing death panel [12].

Jay Michaelson wrote an informative article for The Daily Beast about right-wing hate groups in the US who promote the extreme homophobic legislation in Russia and other countries [13]. It also connects to the Koch brothers who seem to be associated with most evil. Elias Isquith wrote an insightful article for Salon about the current right-wing obsession with making homophobic discrimination an issue of “religious liberty” will hurt religious people [14]. He also describes how stupid the right-wing extremists are in relation to other issues too.

EconomixComix.com has a really great comic explaning the economics of Social Security in the US [15]. They also have a comic explaining the TPP which is really good [16]. They sell a comic book about economics which I’m sure is worth buying. We need to have comics explaining all technical topics, it’s a good way of conveying concepts. When I was in primary school my parents gave me comic books covering nuclear physics and other science topics which were really good.

Mia McKenzie wrote an insightful article for BlackGirlDangerous.com about dealing with racist white teachers [17]. I think that it would be ideal to have a school dedicated to each minority group with teachers from that group.

BTRFS Status July 2014

My last BTRFS status report was in April [1], it wasn’t the most positive report with data corruption and system hangs. Hacker News has a brief discussion of BTRFS which includes the statement “Russell Coker’s reports of his experiences with BTRFS give me the screaming heebie-jeebies, no matter how up-beat and positive he stays about it” [2] (that’s one of my favorite comments about my blog).

Since April things have worked better. Linux kernel 3.14 solves the worst problems I had with 3.13 and it’s generally doing everything I want it to do. I now have cron jobs making snapshots as often as I wish (as frequently as every 15 minutes on some systems), automatically removing snapshots (removing 500+ snapshots at once doesn’t hang the system), balancing, and scrubbing. The fact that I can now expect that a filesystem balance (which is a type of defragment operation for BTRFS that frees some “chunks”) from a cron job and expect the system not to hang means that I haven’t run out of metadata chunk space. I expect that running out of metadata space can still cause filesystem deadlocks given a lack of reports on the BTRFS mailing list of fixes in that regard, but as long as balance works well we can work around that.

My main workstation now has 35 days of uptime and my home server has 90 days of uptime. Also the server that stores my email now has 93 days uptime even though it’s running Linux kernel 3.13.10. I am rather nervous about the server running 3.13.10 because in my experience every kernel before 3.14.1 had BTRFS problems that would cause system hangs. I don’t want a server that’s an hour’s drive away to hang…

The server that runs my email is using kernel 3.13.10 because when I briefly tried a 3.14 kernel it didn’t work reliably with the Xen kernel 4.1 from Debian/Wheezy and I had a choice of using the Xen kernel 4.3 from Debian/Unstable to match the Linux kernel or use an earlier Linux kernel. I have a couple of Xen servers running Debian/Unstable for test purposes which are working well so I may upgrade my mail server to the latest Xen and Linux kernels from Unstable in the near future. But for the moment I’m just not doing many snapshots and never running a filesystem scrub on that server.

Scrubbing

In kernel 3.14 scrub is working reliably for me and I have cron jobs to scrub filesystems on every system running that kernel. So far I’ve never seen it report an error on a system that matters to me but I expect that it will happen eventually.

The paper “An Analysis of Data Corruption in the Storage Stack” from the University of Wisconsin (based on NetApp data) [3] shows that “nearline” disks (IE any disks I can afford) have an incidence of checksum errors (occasions when the disk returns bad data but claims it to be good) of about 0.42%. There are 18 disks running in systems I personally care about (as opposed to systems where I am paid to care) so with a 0.42% probability of a disk experiencing data corruption per year that would give a 7.3% probability of having such corruption on one disk in any year and a greater than 50% chance that it’s already happened over the last 10 years. Of the 18 disks in question 15 are currently running BTRFS. Of the 15 running BTRFS 10 are scrubbed regularly (the other 5 are systems that don’t run 24*7 and the system running kernel 3.13.10).

Newer Kernels

The discussion on the BTRFS mailing list about kernel 3.15 is mostly about hangs. This is correlated with some changes to improve performance so I presume that it has exposed race conditions. Based on those discussions I haven’t felt inclined to run a 3.15 kernel. As the developers already have some good bug reports I don’t think that I could provide any benefit by doing more testing at this time. I think that there would be no benefit to me personally or the Linux community in testing 3.15.

I don’t have a personal interest in RAID-5 or RAID-6. The only systems I run that have more data than will fit on a RAID-1 array of cheap SATA disks are ones that I am paid to run – and they are running ZFS. So the ongoing development of RAID-5 and RAID-6 code isn’t an incentive for me to run newer kernels. Eventually I’ll test out RAID-6 code, but at the moment I don’t think they need more bug reports in this area.

I don’t have a great personal interest in filesystem performance at this time. There are some serious BTRFS performance issues. One problem is that a filesystem balance and subtree removal seem to take excessive amounts of CPU time. Another is that there isn’t much support for balancing IO to multiple devices (in RAID-1 every process has all it’s read requests sent to one device). For large-scale use of a filesystem these are significant problems. But when you have basic requirements (such as a mail server for dozens of users or a personal workstation with a quad-core CPU and fast SSD storage) it doesn’t make much difference. Currently all of my systems which use BTRFS have storage hardware that exceeds the system performance requirements by such a large margin that nothing other than installing Debian packages can slow the system down. So while there are performance improvements in newer versions of the BTRFS kernel code that isn’t an incentive for me to upgrade.

It’s just been announced that Debian/Jessie will use Linux 3.16, so I guess I’ll have to test that a bit for the benefit of Debian users. I am concerned that 3.16 won’t be stable enough for typical users at the time that Jessie is released.