Re: 2.4.7 kernel boot hangs with "cramfs: wrong magic" > In one of your earlier messages, you mentioned turning off DMA. I've > done some searching with google, looked at documentation for kernel and > lilo, and I'm not quite sure how to do that. Would I need to intall > hwtools and hdparm and put put add an hdparm line into > /etc/init.d/whtools? Or is there a way to do this passing parameters > through lilo at boot?
I found a very good introduction to DMA (and how to turn it off) on a web site called exocore.com in India. Although the discussion is about DMA on a RedHat system, most everything probably applies to Debian as well (if anyone on the list thinks otherwise, please let us know in what ways Debian differs). Without further ado: The DMA Issue in RedHat Linux 7.1 by Shanker Balan and Atul Chitnis RedHat ships a highly tuned version of the Linux kernel which enables DMA (Direct Memory Access) or even Ultra DMA on selected IDE controller chipsets. DMA based transfers greatly reduce install time by providing faster file transfer speeds. DMA also reduces CPU usage to a large extent for disk activity. Because of the above mentioned benefits, DMA is a highly desirable feature and in most cases, the DMA enabled kernel works like a charm. (For more on the benefits of using DMA transfers see http://www.linuxdoc.org/HOWTO/mini/Ultra-DMA.html) However, enabling DMA has its downside. It requires that all the components of your system are "healthy". If there is a hardware related problem in any one of the related system components, DMA will fail to function properly. Slow and unreliable installs, CRC errors, file corruptions and even random system lockups are all symptoms of DMA related problems. The most common issues seen are the installer dies when booting, after issuing the message "running: /sbin/loader" installation is extremely slow and often dies at a particular point, but never the same for different users/machines installation suddenly stops complaining about a missing/bad file the CDROM is not accessible after installation Q. Ok, so how can I fix the installation problem? A. To fix the problem, boot off the CD, then, at the boot prompt type linux ide=nodma This disables DMA access while installing. Q. Whew, I disabled DMA with "ide=nodma" and the install completed! But now I seem to be having problems while running normally? Is this also DMA related? A. Most probably yes as the "ide=nodma" option does not disable DMA permanently - it only disables DMA for the current session. Q. So how do I disable DMA permanently? A. Depending on how the CDROM drive has been physically connected to your system, add one of these lines to /etc/rc.d/rc.sysinit: /sbin/hdparm -d0 /dev/hdb # Add this if your CDROM is on primary slave /sbin/hdparm -d0 /dev/hdc # Add this is your CDROM is on secondary master /sbin/hdparm -d0 /dev/hdd # Add this if your CDROM is on secondary slave If you are unsure about the CDROM device id, the "dmesg" output will have it: ~# dmesg|grep CD hdc: ATAPI 48X CDROM, ATAPI CD/DVD-ROM drive hdc: ATAPI 48X CD-ROM drive, 128kB Cache, UDMA(33) Uniform CD-ROM driver Revision: 3.12 In this case, CDROM drive is /dev/hdc. Q.I disabled DMA for the CDROM drive. I still have problems while accessing files. Everything is too slow and the hardisk light remains on for a looong time A. Looks like your harddisk also cannot handle DMA. To disable DMA for a hard drive, add this line to /etc/rc.d/rc.sysinit. /sbin/hdparm -d0 /dev/hda This should cure most DMA related problems. Q. How can I fix DMA related problems so that I can take advantage of its benefits? A. Some of the more common reasons for DMA problems are: Bad or loose IDE connectors. Replacing or securing them usually solves the problem. Broken BIOS. Check with your motherboard/PC manufacturer for DMA related problems with the BIOS. The early Asus P5A motherboards for example had problems in Linux if DMA was enabled. Upgrading the BIOS usually fixes the problem. Broken IDE chipset. This is something which cannot be cured without a hardware change. There are many motherboards shipped with broken controllers which cause data corruption if DMA is enabled. We have one such board in our office. :( See "Are those rumors about buggy interfaces true?" at http://thef-nym.sci.kun.nl/cgi-pieterh/atazip/atafq-3.html#ss3.3 Old IDE devices (hard disks, CDROM drives) don't respond well to DMA. Some drive/controller combinations will work with DMA but not UDMA. You can test this out by playing around with "hdparm" settings. Q. Where can I find out more about Linux and (U)DMA? A. See the The Linux Ultra-DMA Mini-Howto at http://www.linuxdoc.org/HOWTO/mini/Ultra-DMA.html __________________________________________________ Do You Yahoo!? Make international calls for as low as $.04/minute with Yahoo! Messenger http://phonecard.yahoo.com/
