The libata driver in Linux 2.6.12.5 for Intel AHCI chipsets contains a bug. The bug manifests itself as a hard drive light which turns on at the first activity in Linux and does not turn off. The fix is easy.

The SActive bit is set by the driver during each transaction, and the bit causes the HDD LED to light. The device is supposed to reset the bit, but since the bit is only used for NCQ commands, most devices won’t touch the flag unless they are running in NCQ mode. Currently, the production libata driver doesn’t support NCQ, but the driver still assumes the device will unset the SActive bit. The fix is simply to comment out the lines which set the bit in the first place. See more info from LKML. A fix for this is likely to be in 2.6.13, but it should be safe to apply now.

Here are the lines to remove, in function ahci_qc_issue in file drivers/scsi/ahci.c:

writel(1, port_mmio + PORT_SCR_ACT);
readl(port_mmio + PORT_SCR_ACT); /* flush */


UPDATE: This fix is integrated in the recently released 2.6.14 kernel, along with some other AHCI driver fixes.

The new server, colobus.isomerica.net, is now fully assembled and being configured for mail and web and other services. The machine is very loud. It has five fans of variable speed, which can reach 15 thousand rpm. With a bit more configuring she will be ready to move to Switch and Data in Waltham, MA, which will become her new home. From then there will be more configuring and testing and finally a switchover. Check out some more pictures.

Google’s search ranking mechanism PageRank has created a new breed of spam. While email spam is intended for human consumption, unscrupulous “search engine optimizers” use various techniques to get links to their site on your page. This is the genesis of blog comment spam and now referrer spam. By spamming your page with their links, GoogleBot now assumes they are legitimate links and increases the page rank of the linked site.

Referrer spam is when web bots hit your site with the referrer header set to be from the URL they want to link to. When an automated stats package analyzes the web server logs, they will create links to the sites listed in the top referrers. Search engine bots will then scan the page and see the links. It is relatively easy to prevent the web crawlers from seeing the links using robots.txt. However, because of the massive amounts of referrer spam hits, your web stats are now useless.

The solution is to filter the spam hits out of your file using referrercop, a Ruby script written by Ryan Grove. This script uses a blacklist/whitelist of URLs to remove the offending lines from your apache log before it is fed to the stats package. It comes with a default blacklist, which can be easily modified to add new URLs as they appear. Since this filters on the destination URL, not the IP address who made the request, it is impossible to get around using open proxies.

It is still a good idea to block access using robots.txt. If your stats page has previously been spammed with referrer hits you shouldn’t be feeding google with them. Additionally, there is no need for search engines to see the page in any case.

This winter isomerica.net will enter a new era. I have made plans to build a new server, with generously donated hardware, and colocate the server in the Boston metropolitan area. My primary reasons for doing this are stability, bandwidth, and peace of mind.

• Increased Stability
  • The new server will feature true server class stability features, such as ECC memory and redundant storage.
  • The colocation facility will have clean UPS power backed by a generator. Power loss is extremely unlikely.
  • The server will now have redundant, low latency connections to the outside world.
• Better Bandwidth
  • 1Mbps continuous bandwidth will be available, bursting to 100Mbps. This will speed up page loads, especially in the gallery.
  • Lower latency, even during heavy outgoing traffic, will improve the usability of shell sessions and IRC.
• Peace of Mind
  • Should there be problems, such as failed hardware, the server will now be only one hour from me and there will be 24/7 access to the facility.

The planned timeframe is to move services over in early January, 2006. Threepwood will become a workstation only system, gnat will likely be decommissioned. If you currently have DNS services hosted on gnat, these will be moved to the new server which will become NS1.isomerica.net. Secondary DNS can be provided by the bandwidth provider or a third party.

If you currently have an account on threepwood, please let me know any concerns you may have. I would appreciate your comments on the process. During the actual services move there will be a few hours of downtime as final versions of home directory files and email are synced over. If you do not wish to have your data moved, please let me know.

Lastly, I created the isomerica-user mailing list a while back but I haven’t used it for much. Please subscribe to this if you would like to hear further information. Some users may have been subscribed automatically. If you try to sign up and it complains, you’re probably already on the list. Most announcements regarding isomerica.net will be restricted to the mailing list from now on.

This is my brief birthday wishlist. If you’re looking for something to get me, I’d start with the CDs in the Amazon wishlist.

• Merrell Men’s Jungle Moc Nubuck Brown, size 8.5. These are the same Merrell shoes I have now, a present from a few years ago. I love them, but right now the soles are almost completely worn through and the cloth inside is wearing also. I would love a new pair. The exact same shoe. My current ones are the most comfortable shoes I have ever worn.
• Anything from my Amazon wishlist, especially any of the CDs listed there. You don’t have to get them from Amazon, obviously.. it just makes a useful list.
• I just added this to my Amazon wishlist: The Roland Edirol MA-10D Digital Monitor speakers. (Or the MA-20D, but the 10Ds are fine). My computer speakers died a while back, and I have been using my headphones which can be very frustrating. These speakers are designed for quality music listening and can be digitally hooked up to the computer, bypassing the crappy DAC on my sound card (They have a DAC in them).
• The iAudio X5 music player. Yeah, right. I wish :)

Things you should not get me, because I already have one:

• DVD player.

They have apparently developed a taste for Barq’s root beer. More accurately, they have developed a taste for empty soft drink boxes.