From 35c396b859794cac0129ef7d11ad3426bd308a9f Mon Sep 17 00:00:00 2001 From: Nik Clayton Date: Wed, 20 Jun 2001 16:12:33 +0000 Subject: [PATCH] A new article explaining how best to use FreeBSD on solid state media. Submitted by: John Kozubik --- en_US.ISO8859-1/articles/solid-state/Makefile | 24 + .../articles/solid-state/article.sgml | 630 ++++++++++++++++++ 2 files changed, 654 insertions(+) create mode 100644 en_US.ISO8859-1/articles/solid-state/Makefile create mode 100644 en_US.ISO8859-1/articles/solid-state/article.sgml diff --git a/en_US.ISO8859-1/articles/solid-state/Makefile b/en_US.ISO8859-1/articles/solid-state/Makefile new file mode 100644 index 0000000000..9c83b48577 --- /dev/null +++ b/en_US.ISO8859-1/articles/solid-state/Makefile @@ -0,0 +1,24 @@ +# +# $FreeBSD: doc/en_US.ISO8859-1/articles/committers-guide/Makefile,v 1.4 2001/04/08 17:26:59 nik Exp $ +# +# + +DOC?= article + +FORMATS?= html + +INSTALL_COMPRESSED?= gz +INSTALL_ONLY_COMPRESSED?= + +JADEFLAGS+= -V %generate-article-toc% + +# +# SRCS lists the individual SGML files that make up the document. Changes +# to any of these files will force a rebuild +# + +# SGML content +SRCS= article.sgml + +DOC_PREFIX?= ${.CURDIR}/../../.. +.include "${DOC_PREFIX}/share/mk/doc.project.mk" diff --git a/en_US.ISO8859-1/articles/solid-state/article.sgml b/en_US.ISO8859-1/articles/solid-state/article.sgml new file mode 100644 index 0000000000..c694e14cfd --- /dev/null +++ b/en_US.ISO8859-1/articles/solid-state/article.sgml @@ -0,0 +1,630 @@ + + + +%man; + +]> + +
+ + FreeBSD and Solid State Devices + + + + John + Kozubik + + +
john@kozubik.com
+ + + + + $FreeBSD$ + + + 2001 + The FreeBSD Documentation Project + + + &legalnotice; + + + This article covers the use of solid state disk devices in FreeBSD + to create embedded systems. + + Embedded systems have the advantage of increased stability due to + the lack of integral moving parts (hard drives). Account must be + taken, however, for the generally low disk space available in the + system and the durability of the storage medium. + + Specific topics to be covered include the types and attributes of + solid state media suitable for disk use in FreeBSD, kernel options + that are of interest in such an environment, the + rc.diskless mechanisms that automate the + initialization of such systems and the need for read-only filesystems, + and building file systems from scratch. The article will conclude + with some general strategies for small and read-only FreeBSD + environments. + + + + + Solid State Disk Devices + + The scope of this article will be limited to solid state disk + devices made from flash memory. Flash memory is a solid state memory + (no moving parts) that is non-volatile (the memory maintains data even + after all power sources have been disconnected). Flash memory can + withstand tremendous physical shock and is reasonably fast (the flash + memory solutions covered in this article are slightly slower than a EIDE + hard disk for write operations, and much faster for read operations). + One very important aspect of flash memory, the ramifications of which + will be discussed later in this article, is that each sector has a + limited rewrite capacity. You can only write, erase, and write again to + a sector of flash memory a certain number of times before the sector + becomes permanently unusable. Although many flash memory products + automatically map bad blocks, and although some even distribute write + operations evenly throughout the unit, the fact remains that there + exists a limit to the amount of writing that can be done to the device. + Competitive units have between 1,000,000 and 10,000,000 writes per + sector in their specification. This figure varies due to the + temperature of the environment. + + Specifically, we will be discussing ATA compatible compact-flash + units and the M-Systems Disk-On-Chip flash memory unit. ATA compatible + compact-flash cards are quite popular as storage media for digital + cameras. Of particular interest is the fact that they pin out directly + to the IDE bus and are compatible with the ATA command set. Therefore, + with a very simple and low-cost adaptor, these devices can be attached + directly to an IDE bus in a computer. Once implemented in this manner, + operating systems such as FreeBSD see the device as a normal hard disk + (albeit small). The M-Systems Disk-On-Chip product is based on the same + underlying flash memory technology as ATA compatible compact-flash + cards, but resides in a DIP form factor and is not ATA compatible. To + use such a device, not only must you install it on a motherboard that + has a Disk-On-Chip socket, you must also build the `fla` driver into any + FreeBSD kernel you wish to use it with. Further, there is critical, + manufacturer-specific data residing in the boot sector of this device, + so you must take care not to install the FreeBSD (or any other) boot + loader when using this. + + Other solid state disk solutions do exist, but their expense, + obscurity, and relative unease of use places them beyond the scope of + this article. + + + + Kernel Options + + A few kernel options are of specific interest to those creating + an embedded FreeBSD system. + + First, all embedded FreeBSD systems that use flash memory as system + disk will be interested in memory disks and memory filesystems. Because + of the limited number of writes that can be done to flash memory, the + disk and the filesystems no the disk will most likely be mounted + read-only. In this environment, filesystems such as + /tmp and /var are mounted as + memory filesystems to allow the system to create logs and update + counters and temporary files. Memory filesystems are a critical + component to a successful solid state FreeBSD implementation. + + You should make sure the following lines exist in your kernel + configuration file: + + options MFS # Memory Filesystem +options MD_ROOT # md device usable as a potential root device +pseudo-device md # memory disk + + Second, if you will be using the M-Systems Disk-On-Chip product, you + must also include this line: + + device fla0 at isa? + + + + <filename>rc.diskless</filename> and Read-Only Filesystems + + The post-boot initialization of an embedded FreeBSD system is + controlled by /etc/rc.diskless2 + (/etc/rc.diskless1 is for BOOTP diskless boot). + This initialization script is invoked by placing a line in + /etc/rc.conf as follows: + + diskless_mount=/etc/rc.diskless2 + + rc.diskless2 mounts /var + as a memory filesystem, makes a configurable list of directories in + /var with the &man.mkdir.1; command, changes modes + on some of those directories, and extracts a list of device entries to + copy to a writable (again, a memory filesystem) + /dev partition. In the execution of + /etc/rc.diskless2, one other + rc.conf variable comes into play - + varsize. The /etc/rc.diskless2 + file creates a /var partition based on the value of + this variable in rc.conf: + + varsize=8192 + + Remember that this value is in sectors. The creation of the + /dev partition by + /etc/rc.diskless2, however, is governed by a + hard-coded value of 4096 sectors. It is trivial to change this entry in + the /etc/rc.diskless2 file itself, although you + shouldn't need more space than that for + /dev. + + It is important to remember that the + /etc/rc.diskless2 script assumes that you have + already removed your conventional /tmp partition + and replaced it with a symbolic link to /var/tmp. + Because tmp is one of the directories created in + /var by the /etc/rc.diskless2 + script, and because /var is a memory file system + (which is mounted read-write), /tmp will now be a + directory that is read-write as well. + + The fact that /var and + /dev are read-write filesystems is an important + distinction, as the / partition (and any other + partitions you may have on your flash media) should be mounted + read-only. Remember that in we detailed the + limitations of flash memory - specifically the limited write capability. + The importance of not mounting filesystems on flash media read-write, + and the importance of not using a swap file cannot be overstated. A + swap file on a busy system can burn through a piece of flash media in + less than one year. Heavy logging or temporary file creation and + destruction can do the same. Therefore, in addition to removing the + swap and /proc entries from your + /etc/fstab file, you should also change the Options + field for each filesystem to ro as follows: + + # Device Mountpoint FStype Options Dump Pass# +/dev/ad0s1a / ufs ro 1 1 + + A few applications in the average system will immediately begin to + fail as a result of this change. For instance, ports will not install + from the ports tree because the + /var/db/port.mkversion file does not exist. cron + will not run properly as a result of missing cron tabs in the + /var created by + /etc/rc.diskless2, and syslog and dhcp will + encounter problems as well as a result of the read-only filesystem and + missing items in the /var that + /etc/rc.diskless2 has created. These are only + temporary problems though, and are addressed, along with solutions to + the execution of other common software packages in + . + + An important thing to remember is that a filesystem that was mounted + read-only with /etc/fstab can be made read-write at + any time by issuing the command: + + &prompt.root; /sbin/mount -uw partition + + and can be toggled back to read-only with the command: + + &prompt.root; /sbin/mount -ur partition + + + + Building a File System From Scratch + + Because ATA compatible compact-flash cards are seen by FreeBSD as + normal IDE hard drives, as is a M-Systems Disk-On-Chip product (when you + are running a kernel with the fla driver built in) you could + theoretically install FreeBSD from the network using the kern and + mfsroot floppies or from a CD. Other than the fact that you should not + write a boot-loader of any kind to the M-Systems device, no special + instructions are needed. + + However, even a small installation of FreeBSD using normal + installation procedures can produce a system in size of greater than 200 + megabytes. Because most people will be using smaller flash memory + devices (128 megabytes is considered fairly large - 32 or even 16 + megabytes is common) an installation using normal mechanisms is not + possible—there is simply not enough disk space for even the + smallest of conventional installations. + + The easiest way to overcome this space limitation is to install + FreeBSD using conventional means to a normal hard disk. After the + installation is complete, pare down the operating system to a size that + will fit onto your flash media, then tar the entire filesystem. The + following steps will guide you through the process of preparing a piece + of flash memory for your tarred filesystem. Remember, because a normal + installation is not being performed, operations such as partitioning, + labeling, file-system creation, etc. need to be performed by hand. In + addition to the kern and mfsroot floppy disks, you will also need to use + the fixit floppy. If you are using a M-Systems Disk-On-Chip, the kernel + on your kern floppy must have the fla option detailed + in compiled into it. Please see + for instructions on creating a new kernel for + kern.flp. + + + + Partitioning your flash media device + + After booting with the kern and mfsroot floppies, choose + custom from the installation menu. In the custom + installation menu, choose partition. In the + partition menu, you should delete all existing partitions using the + d key. After deleting all existing partitions, + create a partition using the c key and accept the + default value for the size of the partition. When asked for the + type of the partition, make sure the value is set to + 165. Now write this partition table to the disk + by pressing the w key (this is a hidden option on + this screen). When presented with a menu to choose a boot manager, + take care to select None if you are using an + M-Systems Disk-On-Chip. If you are using a ATA compatible compact + flash card, you should choose the FreeBSD Boot Manager. Now press + the q key to quit the partition menu. You will be + shown the boot manager menu once more - repeat the choice you made + earlier. + + + + Creating file systems on your flash memory device + + Exit the custom installation menu, and from the main + installation menu choose the fixit option. After + entering the fixit environment, enter the following commands: + + + + + + ATA compatible + + Disk-On-Chip + + + + + &prompt.root; mknod /dev/ad0c c 116 0 +&prompt.root; mknod /dev/ad0c c 116 2 +&prompt.root; disklabel -e /dev/ad0c + + &prompt.root; mknod /dev/fla0c c 102 2 +&prompt.root; mknod /dev/fla0c c 102 2 +&prompt.root; disklabel -e /dev/fla0c + + + + + + At this point you will have entered the vi editor under the + auspices of the disklabel command. If you are using Disk-On-Chip, + the first step will be to change the type value near the beginning + of the file from ESDI to + DOC2K. Next, regardless of whether you are using + Disk-On-Chip or ATA compatible compact flash media, you need to add + an a: line at the end of the file. This a: line + should look like: + + a: 123456 0 4.2BSD 0 0 + + Where 123456 is a number that is + exactly the same as the number in the existing c: + entry for size. Basically you are duplicating the existing + c: line as an a: line, making + sure that fstype is 4.2BSD. Save the file and + exit. + + + + + + ATA compatible + + Disk-On-Chip + + + + + &prompt.root; disklabel -B -r /dev/ad0c +&prompt.root; newfs /dev/ad0a + + &prompt.root; disklabel -B -r /dev/fla0c +&prompt.root; newfs /dev/fla0a + + + + + + + + Placing your filesystem on the flash media + + Mount the newly prepared flash media: + + + + + + ATA compatible + + Disk-On-Chip + + + + + &prompt.root; mount /dev/ad0a /flash + + &prompt.root; mount /dev/fla0 /flash + + + + + + Bring this machine up on the network so we may transfer our tar + file and explode it onto our flash media filesystem. One example of + how to do this is: + + &prompt.root; ifconfig xl0 192.168.0.10 netmask 255.255.255.0 +&prompt.root; route add default 192.168.0.1 + + Now that the machine is on the network, transfer your tar file. + You may be faced with a bit of a dilemma at this point - if your + flash memory part is 128 megabytes, for instance, and your tar file + is larger than 64 megabytes, you cannot have your tar file on the + flash media at the same time as you explode it - you will run out of + space. One solution to this problem, if you are using ftp, is to + untar the file while it is transferred over ftp. If you perform + your transfer in this manner, you will never have the tar file and + the tar contents on your disk at the same time: + + ftp> get tarfile.tar "| tar xvf -" + + If your tarfile is gzipped, you can accomplish this as + well: + + ftp> get tarfile.tar "| zcat | tar xvf -" + + After the contents of your tarred filesystem are on your flash + memory file system, you can unmount the flash memory and + reboot: + + &prompt.root; cd / +&prompt.root; umount /flash +&prompt.root; exit + + Assuming that you configured your filesystem correctly when it + was built on the normal hard disk (with your filesystems mounted + read-only, and with the necessary options compiled into the kernel) + you should now be successfully booting your FreeBSD embedded + system. + + + + + + Building a <filename>kern.flp</filename> Installation Floppy with + the fla Driver + + + This section of the article is relevant only to those using + M-Systems Disk-On-Chip flash media. + + + It is possible that your kern.flp boot floppy + does not have a kernel with the fla driver + compiled into it necessary for the system to recognize the Disk-On-Chip. + If you have booted off of the installation floppies and are told that no + disks are present, then you are probably lacking the + fla driver in your kernel. + + After you have built a kernel with fla + support that is smaller than 1.4 megabytes, you can create a custom + kern.flp floppy image with it by following these + instructions: + + + + Obtain an existing kern.flp image file + + + + &prompt.root; vnconfig vn0c kern.flp + + + + &prompt.root; mount /dev/vn0c /mnt + + + + Place your kernel file into /mnt, replacing + the existing one + + + + &prompt.root; vnconfig -d vn0c + + + + Your kern.flp file now has your new kernel on it. + + + + System Strategies for Small and Read Only Environments + + In , it was pointed out that the + /var filesystem constructed by + /etc/rc.diskless2 and the presence of a read-only + root filesystem causes problems with many common software packages used + with FreeBSD. In this article, suggestions for successfully running + cron, syslog, ports installations, and the Apache web server will be + provided. + + + cron + + In /etc/rc.diskless2 there is a variable + named var_dirs. This variable consists of a + space-delimited list of directories that will be created inside of + /var after it is mounted as a memory filesystem. + cron and cron/tabs are not + in that list, and without those directories, cron will complain. By + inserting cron, cron/tabs, and + perhaps even at, and at/jobs as + elements of that variable, you will facilitate the running of the + &man.cron.8; and &man.at.1; daemons. + + However, this still does not solve the problem of maintaining cron + tabs across reboots. When the system reboots, the + /var filesystem that is in memory will disappear + and any cron tabs you may have had in it will also disappear. + Therefore, one solution would be to create cron tabs for the users + that need them, mount your / filesystem as + read-write and copy those cron tabs to somewhere safe, like + /etc/tabs, then add a line to the end of + /etc/rc.diskless2 that copies those crontabs into + /var/cron/tabs after that directory has been + created during system initialization. You may also need to add a line + that changes modes and permissions on the directories you create and + the files you copy with /etc/rc.diskless2. + + + + syslog + + syslog.conf specifies the locations of + certain log files that exist in /var/log. These + files are not created by /etc/rc.diskless2 upon + syste initialization. Therefore, somewhere in + /etc/rc.diskless2, after the section that creates + the directories in /var, you will need to add + something like this: + + &prompt.root; touch /var/log/security /var/log/maillog /var/log/cron /var/log/messages +&prompt.root; chmod 0644 /var/log/* + + You will also need to add the log directory to the list of + directories that /etc/rc.diskless2 + creates. + + + + ports installation + + Before discussing the changes necessary to successfully use the + ports tree, a reminder is necessary regarding the read-only nature of + your filesystems on the flash media. Since they are read-only, you + will need to temporarily mount them read-write using the mount syntax + shown in . You should always remount those + filesystems read-only when you are done with any maintenance - it is + dangerous to leave them in read-write mode lest a process begin + logging or otherwise writing regularly to the flash media and wearing + it out over time. + + To make it possible to enter a ports directory and successfully + run make install, it is necessary for the file + /var/db/port.mkversion to exist, and that it have + a correct date in it. Further, we must create a packages directory on + a non-memory filesystem that will keep track of our packages across + reboots. Because it is necessary to mount your filesystems as + read-write for the installation of a package anyway, it is sensible to + assume that an area on the flash media can also be used for package + information to be written to. + + First, create a package database directory. This is normally in + /var/db/pkg, but we cannot place it there as it + will disappear every time the system is booted. + + &prompt.root; mkdir /etc/pkg + + Now, add a line to /etc/rc.diskless2 that + links the /etc/pkg directory to + /var/db/pkg. An example: + + &prompt.root; ln -s /etc/pkg /var/db/pkg + + Add another line in /etc/rc.diskless2 that + creates and populates + /var/db/port.mkversion + + &prompt.root; touch /var/db/port.mkversion +&prompt.root; chmod 0644 /var/db/port.mkversion +&prompt.root; echo 20010412 >> /var/db/port.mkversion + + where 20010412 is a date that is + appropriate for your particular release of FreeBSD + + Now, any time that you mount your file systems as read-write and + install a package, the make install will work + because it finds a suitable + /var/db/port.mkversion, and package information + will be written successfully to /etc/pkg (because + the filesystem will, at that time, be mounted read-write) which will + always be available to the operating system as + /var/db/pkg. + + + + Apache Web Server + + Apache keeps pid files and logs in + apache_install/logs. + Since this directory no doubt exists on a read-only file system, this + will not work. It is necessary to add a new directory to the + /etc/rc.diskless2 list of directories to create + in /var, to link + apache_install/logs to + /var/log/apache. It is also necessary to set + permissions and ownership on this new directory. + + First, add the directory log/apache to the list + of directories to be created in + /etc/rc.diskless2. + + Second, add these commands to + /etc/rc.diskless2 after the directory creation + section: + + &prompt.root; chmod 0774 /var/log/apache +&prompt.root; chown nobody:nobody /var/log/apache + + Finally, remove the existing + apache_install/logs + directory, and replace it with a link: + + &prompt.root; rm -rf (apache_install)/logs +&prompt.root; ln -s /var/log/apache (apache_install)/logs + + +
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