Advanced filesystem implementor's guide, Part 10
This content is part # of # in the series: Common threads
This content is part of the series:Common threads
Stay tuned for additional content in this series.
In this article, I'll show you how to get XFS up and running on your system. First, make sure that you're aware of and have explored the SGI XFS Project page (see Related topics later in this article). If you follow the download link, you'll find patches, tools, and even Red Hat XFS-enabled kernels.
But wait. While it is possible to install XFS using these pre-rolled, official releases, I don't recommend this approach. At the time this article was written, the most recent official release of XFS was 1.0.2, which was released way back in November 2001. A lot of improvements have been made to XFS since then, and in order to benefit from those improvements, it's best to use the up-to-date sources from the XFS CVS tree. Based on feedback from Gentoo Linux developers and users, those who have used XFS from CVS have had a much more positive XFS experience than those who have tried using the slightly outdated official releases.
If you've never used CVS before, you might be interested in my tutorial, CVS
for the developer or amateur (see Related topics). If you'd rather just "wing it" and follow along, well, that's okay too. Just make sure that you have a CVS package of some kind
installed on your system so that you can use the
The CVS instructions I provide here can also be found on SGI's site (see
Related topics). When you're done grabbing your sources via
cvs, you'll have a new directory tree that contains
up-to-date XFS-enabled kernel sources and the latest XFS tools. To grab the
sources from XFS CVS, first set the
environment variable to the repository from which you need to grab the sources.
At the bash prompt, type:
$ export CVSROOT=':pserver:email@example.com:/cvs'
Now, change directories to where you'd like the new XFS directory tree to be created, and type:
$ cvs login
When prompted for a password, type
now logged in to the public CVS repository; to get the most recent
XFS sources, type:
$ cvs -z3 checkout linux-2.4-xfs
The checkout process will begin. It may take a while, since the files
you're grabbing include a complete Linux source tree. After a while, the
cvs checkout command will complete and you'll have a new
linux-2.4-xfs directory tree in your current working
directory. For future reference, if you ever need to update your new source
tree, simply enter the
linux-2.4-xfs directory and
$ cvs -z3q update -dP
Using the tree
Two important directories are inside the new
linux-2.4-xfs directory. The first is called
linux and contains an XFS-enabled kernel source tree, and
the second is called
cmd and includes sources for
the various XFS userspace programs. To use the kernel sources, you can either
linux directory to
/usr/src or simply compile a new kernel in place.
Here's how to get this kernel up and running. Enter the
linux directory and load
Makefile into your favorite editor. At the top of
the file, you'll see a few lines that look like this:
VERSION = 2 PATCHLEVEL = 4 SUBLEVEL = 17 EXTRAVERSION = -xfs
These lines tell the
Makefile to build a kernel
with the official name
2.4.17-xfs. Some prefer
having a kernel without an
-xfs in the official
uname -a kernel name; if you're one of these people,
then change the last line to read:
Now for kernel configuration. To enable XFS, type
make menuconfig and head over to the File systems section. Scroll down a bit and you'll see
the following option:
< > SGI XFS filesystem support
Enable it (compiling it directly into your kernel is recommended). Hit
y, and the following three sub-options will appear:
[ ] Enable XFS Realtime support [ ] Enable XFS Quota < > Enable XFS DMAPI
The "XFS Realtime" option will enable realtime subvolume support in XFS, which lets you configure storage areas that can provide more deterministic performance for realtime applications. The "XFS Quota" option will -- you guessed it -- enable support for associating disk usage limits with certain users and groups. The "XFS DMAPI" option, if selected, will enable a special API that is intended for use by storage management applications. Currently, no production Linux tools take advantage of DMAPI (this includes Sistina's LVM as well as the SGI XFS utilities themselves); however, some DMAPI-enabled applications are currently in development by SGI and IBM.
Once you've selected "SGI XFS filesystem support" and the rest of the kernel is
configured the way you like it, you're ready to
make dep &&
make bzImage && make modules && make modules_install, install your
kernel, and reboot.
Installing the tools
Now that your XFS-enabled kernel is up and running, you can get the various
XFS tools installed. One of the nice things about XFS is that it comes with a
fairly comprehensive suite of support tools and utilities. Enter the
linux-2.4-xfs/cmd directory and type the following shell
script at the bash prompt as the "root" user:
# for x in attr acl xfsprogs dmapi xfsdump do cd $x autoconf /configure --prefix=/usr make make install cd .. done
After you type the last
done line, our ad hoc
build script will begin executing, and all the various XFS tools will be
installed. Now, you can finish up by installing a few
developer-related files that weren't installed by the previous
make install commands:
# for x in attr dmapi xfsprogs do cd $x make install-dev cd .. done
Creating and mounting the filesystem
Once this final script completes, all the various XFS-related programs should be properly installed and ready for use. Now you're ready to create a test XFS filesystem tweaked for optimal performance.
But first, if you're creating an XFS filesystem on top of what was previously a ReiserFS filesystem, you'll need to perform a small trick. At the bash prompt, use the following command to "zero out" the beginning of the block device that was used to store the ReiserFS filesystem and is about to be initialized to contain your new XFS filesystem:
# dd if=/dev/zero of=/dev/hdc9
This step is necessary in order to wipe out any remaining ReiserFS metadata;
mount can get confused and accidentally
mount your new XFS filesystem as a defective ReiserFS filesystem! You should
only need to let
dd run for about 10 seconds, after
which you can abort the command with a control-C. At this point, the critical
portions of the pre-existing ReiserFS metadata will be zeroed out, and
mount's filesystem-type autodetection code won't get
Now it's time to create a new filesystem. To do this, you could use
mkfs.xfs as follows:
# mkfs.xfs /dev/hdc9
While the above command will work, there are a couple of options that you might want to
mkfs.xfs to configure your new XFS
filesystem for maximum performance.
The first such option is
-l size=32m, which tells
mkfs.xfs to configure your filesystem so that it has a
hefty 32 MB metadata journal. This improves performance by making it less
likely that your metadata journal will "fill up" during heavy filesystem usage.
The second option lets you enhance the performance of your new filesystem by telling
mkfs.xfs to minimize the number of allocation
groups that are created. Normally,
the number of allocation groups automatically, but from my experience it
usually picks a number that is a bit too high for most general-purpose Linux
workstations and servers. As you'll recall from my
previous article, allocation groups let XFS perform multiple metadata
operations in parallel. This comes in handy on high-end servers, but too many
allocation groups do add a bit of overhead. So rather than let
mkfs.xfs choose the number of allocation groups for your
filesystem, specify a number by using the
-d agcount=x option. Set
x to a small number, something like 4, 6, or 8. You'll need
at least one allocation group for every 4 GB of capacity in your target block
device. Putting these two tweaks together, create an "optimized" XFS
filesystem using the following command:
# mkfs.xfs -d agcount=4 -l size=32m /dev/hdc9
Now that your filesystem is created, you can mount it. When doing so, you'll use some performance-enhancing mount options to squeeze the last ounce of performance out of your new filesystem:
# mount /dev/hdc9 /mnt -o noatime,nodiratime,osyncisdsync
The first two mount options turn off
atime updates, which are very rarely
needed and serve little purpose other than to degrade filesystem performance. The
osyncisdsync option tweaks XFS's sync/async behavior so that it is more
in line with that of ext3. Thanks to our
mount tweaks, your new XFS filesystem will
perform much better than it would have otherwise.
One of the nice things about XFS is that it includes a lot of goodies. One of these goodies is some special functionality called "access control lists" or ACLs, and is now enabled on XFS filesystems by default. Access control lists let you define fine-grained permissions for files. For example, rather than simply being limited to defining "rwx" access for user, group, and all others, you can now add any number of additional users or groups and specify "rwx" permissions for them as well.
Full coverage of access control lists is beyond the scope of this article, but you can find a great introduction to ACLs on the bestbits site (see Related topics), particularly if you go to the "Why you may want Access Control Lists (ACLs)" page. Note that most of the in-depth technical information on that site is related to enabling ACL support under ext2 and ext3 (but no additional steps are needed to get ACLs working on XFS filesystems).
XFS includes another neat feature called "extended attributes." Extended
attributes let you associate user-defined data with filesystem objects.
For example, if you had a graphic called
mygraphic.png, you could attach an attribute called
"thumbnail" that contained a small version of the image. This data wouldn't be
viewable by normal file IO operations but could be accessed by any program
using a special extended attributes API. In a way, extended attributes
resemble the "resource fork" that exists on MacOS systems.
Here's an example of how to interact with extended attributes using the
attr command line executable. Let's say I wanted to
description attribute to my home directory. I
$ attr -s description -V "Home of Daniel Robbins" /home/drobbins Attribute "description" set to a 22 byte value for /home/drobbins: Home of Daniel Robbins
Then, to see a list of the attributes associated with
/home/drobbins, I could type:
$ attr -l /home/drobbins Attribute "description" has a 22 byte value for /home/drobbins/
And, to view the contents of the
attribute, I'd type:
$ attr -q -g description /home/drobbins/ Home of Daniel Robbins
Extended attributes are easy and fun to use. You can learn more
about them by typing
man attr. XFS includes a C API
for interacting with extended attributes as well. If you're interested in
working with a C++ IOStream interface to extended attributes, you may want to check out libferris on SourceForge (see Related topics).
Yes, extended attributes and ACLs are really fun, but beware -- most backup
programs currently still ignore EA and ACL data. Notable exceptions are the
commands included with the XFS distribution. If you're using any other backup
program, be sure to do a bit of research before using extended attributes and
ACLs all over the place.
I hope you've enjoyed this whirlwind introduction to the XFS filesystem. See you next article!
- Read Daniel's previous articles in this series, where he describes:
- The benefits of journalling and ReiserFS (Part 1)
- Setting up a ReiserFS system (Part 2)
- Using the tmpfs virtual memory filesystem and bind mounts (Part 3)
- Beginning the conversion to devfs (Part 5)
- Completing the conversion to devfs using an init wrapper (Part 6)
- The benefits of the ext3 filesystem (Part 7)
- An in-depth look at ext3 and the latest kernel updates (Part 8)
- You can learn more about XFS at SGI's XFS Project page. Read the FAQ. Join the mailing list. Download the software.
- Familiarize yourself with access control lists at the Extended attributes and access control lists page.
- IBM's JFS is an alternative journaled file system licensed under the GNU General Public License. For more information, go to the JFS for Linux home page.
- Browse more Linux resources on developerWorks.
- Browse more Open source resources on developerWorks.