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<FONT FACE="ARIAL NARROW, HELVETICA" SIZE="5"><B>Linux XFS FAQ</B></FONT>
<FONT FACE="ARIAL NARROW, HELVETICA">
<h2>
Q: Where can I find this FAQ?
</h2>
<P>
Currently at:
</P>
<ul>
    <A HREF="http://oss.sgi.com/projects/xfs/faq.html">http://oss.sgi.com/projects/xfs/faq.html</A>
</ul>
<P>
If you have any comments or suggestions just let me know:
</P>
<ul>
    <A HREF="mailto:thomas.graichen@innominate.de">thomas.graichen@innominate.de</A>
</ul>
<h2>
Q: What is XFS?
</h2>
<P>
XFS is a journalling filesystem developed by SGI and used in SGI's
IRIX operating system. It is now also available under GPL for linux. 
It is extremely scalable, using btrees extensively to support large
and/or sparse files, and extremely large directories. The journalling
capability means no more waiting for fsck's or worrying about meta-data
corruption.
</P>
<h2>
Q: Where can I find information about XFS for linux?
</h2>
<P>
Just point your web-browser to:
</P>
<ul>
    <A HREF="http://oss.sgi.com/projects/xfs/">http://oss.sgi.com/projects/xfs/</A>
</ul>
<h2>
Q: What do I need to build an XFS ready kernel?
</h2>
<P>
The best way to do this is to checkout the SGI XFS kernel from
their CVS tree. How to do this is described at
</P>
<ul>
    <A HREF="http://oss.sgi.com/projects/xfs/cvs_download.html">http://oss.sgi.com/projects/xfs/cvs_download.html</A>
</ul>
<P>
After that you have two subtrees of importance: linux and cmd. The
firsts one - linux - is a normal linux kernel source tree containing
the XFS code. It is updated to the latest available linux kernel
from time to time but it may be a bit (not much) behind. Just build
your kernel the way you are used to do it and don't forget to enable
XFS and pagebuf under filesystems. You also need to enable the
ask for experimental features option in the "Code maturity level
options" menu. Also keep in mind that currently
the option for using kiobufs only works on scsi drives. The other
tree - cmd - contains all the tools you need - most important:
<tt>mkfs.xfs</tt> and <tt>xfs_repair</tt> - just go to the xfs subdirectory in cmd
and type make (maybe followed by make install to install the
binaries). One thing which is also important to note is that
you need to have the e2fs-devel package installed in order to
build the cmd tools - because they require the uuid stuff in
them. You may also build src and binary rpms by running:
</P>
<pre>
    ./Makepkgs verbose
</pre>
<P>
in the cmd/xfs directory.  The tools also have
man-pages which you may consult for interesting options like:
</P>
<pre>
    mkfs -t xfs -l size=16000b /dev/foo
</pre>

<P>
which sets the log size within the filesystem.
There exists also another way to get an XFS ready kernel - you may
get kernel patches relative to a official kernel from:
</P>
<ul>
    <A HREF="ftp://oss.sgi.com/projects/xfs/download">ftp://oss.sgi.com/projects/xfs/download</A>
</ul>
<P>
and apply then to the kernel sources the patch is for. This is a
good way for all the people who don't want to use CVS or do not
have the bandwidth to checkout the whole kernel tree.
</P>
<h2>
Q: How do I use XFS?
</h2>
<P>
Just reboot the new build kernel and create a filesytem on an empty
partition
</P>
<pre>
    mkfs -t xfs /dev/foo
</pre>
<P>
where /dev/foo is the the partition you want to use (you may have
to use the -f option of <tt>mkfs -t xfs</tt> (which calls mkfs.xfs from
the cmd directory which you must have installed) if this partition already con-
tains an old filesystem which you want to overwrite). Now you can
mount the filesystem using:
</P>
<pre>
    mount -t xfs /dev/foo /somewhere
</pre>
<h2>
Q: How stable is XFS?
</h2>
<P>
It is quite useable now but I would not recommend it for production
use right now - but I think it will be there quite soon. I am using
it here in a test scenario for a 50 people squid and a ~20 mb/day
newsfeed with 30 simulated users on an XFS only machine and had no
problems so far. Also SGI is doing quite a lot of stress tests with
it (see the stress subdir of the cmd tree).
</P>
<h2>
Q: Does it run on platforms other than i386?
</h2>
<P>
The current XFS tree seems to work just fine on ppc now (aside from some
trivial compile fixes). There is also work underway to get it to that
state on the alpha and the sparc64 too which looks very promising. All
in all it looks like XFS will be running across a lot of platforms
fine soon. Also an important note is that XFS is inherently platform
independent in the on disk layout - so it should be possible to move
a XFS disk from one linux platform to another out of the box.
</P>
<P>
If you are interested in this you may have a look at
</P>
<ul>
    <A HREF="http://innominate.org/~graichen/projects/xfs/">http://innominate.org/~graichen/projects/xfs/</A>
</ul>
<h2>
Q: Do quotas work on XFS?
</h2>
<P>
With the right tools, yes. Work on user quotas is almost complete and
should be in a release soon.
</P>
<h2>
Q: Is there any dump/restore for XFS?
</h2>
<P>
xfsdump and xfsrestore are now in the CVS tree. The tape format is
the same as for xfsdump and xfsrestore on IRIX and dump tapes should
be interchangable between systems. 
</p>
<p>
The tape format is <em>not the same</em> as the classic Unix dump but should 
work fine with tools like Amanda. Dumps produced with standard 
other dump programs should be able to be restored onto an XFS filesystem 
using the coresponding restore program.
</P>
<h2>
Q: Does LILO work with XFS?
</h2>
<P>
Yes
</P>
<h2>
Q: Does GRUB work with XFS?
</h2>
<P>
No - so far there is no direct support in GRUB to boot from an XFS
filesystem but you may still boot an mostly XFS system with a small
ext2 /boot partition with all the GRUB stuff on it using GRUB. Btw.
writing XFS support for GRUB would be a good way to learn more about
XFS if anyone is interested :-).
</P>
<h2>
Q: Can I run XFS on top of LVM?
</h2>
<P>
Yes you can but you need to use a patch for LVM because the XFS
kernel contains stephen tweedies sard patches which change the
format of /proc/partitions. Also for using XFS on LVM you should
not enable the kiobuf option in the kernel XFS compile options.
You may get a patch (created by William L Jones) to start from at
</P>
<ul>
    <A HREF="http://innominate.org/~graichen/projects/xfs/lvm.patch">http://innominate.org/~graichen/projects/xfs/lvm.patch</A>
</ul>
<P>
See the head of it for details and a list of contributors.
</P>
<h2>
Q: Can I use XFS on loopback block devices?
</h2>
<P>
Yes.
</P>
<h2>
Q: Can XFS be used for a root filesystem?
</h2>
<P>
Yes. The only problem is boot-strapping the process. Steps are being
taken to make this process easier.
</P>
<h2>
Q: What partition type should I use for XFS? 
</h2>
<P>
Linux native filesystem (83).
</P>
<h2>
Q: Mounting the XFS filesystem does not work - what is wrong?
</h2>
<P>
If you get something like:
</P>
<pre>
    mount: /dev/hda5 has wrong major or minor number
</pre>
<P>
you either don't have XFS compiled into the kernel (or you forgot
to load the modules) or you did not use the "-t xfs" option on mount
or the "xfs" option in <tt>/etc/fstab</tt>.
</P>
<h2>
Q: Does XFS run with the linux software RAID md driver?
</h2>
<P>
Nobody has tested it so far but expect it not to work like for
all the other journaling filesystems due to internal buffer locking
problems I think. If anyone tries this - please let me know.
Also keep in mind - if you want to try it - also the md driver
will definitely not work with the kiobuf option enabled.
</P>
<h2>
Q: Does XFS run on hardware RAID?
</h2>
<P>
Yes - hardware RAID is like a normal disk to XFS (like to any other
filesystem) and this should not be a problem.
</P>
<h2>
Q: Can I run NFS on top of an XFS partition?
</h2>
<P>
Yes. However there may be some remaining issues under heavy load.
</P>
<h2>
Q: Is there a way to resize an XFS filesystem?
</h2>
<P>
An XFS filesystem may be enlarged within a partition using 
<tt>xfs_growfs</tt>.  Back up your filesystem before using this
tool.
</P>
<h2>
Q: Will I be able to use my old IRIX XFS disks on linux?
</h2>
<P>
Yes. The on-disk format of XFS is the same on IRIX and Linux. Obviously,
you should back-up your data before trying to move it between systems.
Filesystems must be "clean" when moved (ie unmounted correctly).
</p>
<p>
The only real caveat here is that at the moment XFS on linux only supports
filesystems where the disk block size equals the page size. Support
for other block sizes available on IRIX is work-in-progress.
</P>
<h2>
Q: Is there documentation on how XFS works?
</h2>
<P>
There are some papers available on the SGI XFS project page (mentioned
above) and I have set up an LXR indexed version of the SGI XFS CVS tree
at:
</P>
<ul>
    <A HREF="http://innominate.org/~graichen/projects/lxr/source/?v=xfs">http://innominate.org/~graichen/projects/lxr/source?v=xfs</A>
</ul>
<P>
which might help to find an easy and good way through
the sources. I plan to keep this tree automatically updated to the
current SGI XFS CVS version on a daily basis within the next days.
If anyone has pointers to other XFS related docs - just send me a
mail (address - see above).
</P>
<h2>
Q: Processes are hanging when acting on an XFS filesystem (for
instance in sv_wait) - what is this?
</h2>
<p>
Recompile your kernel with gcc 2.91.66 instead of gcc 2.95 this should
fix your problem.
</P>
<h2>
Q: Are there any known issues about gcc 2.95 for compiling the
XFS kernel tree?
</h2>
<p>
Yes. So far there were some problems reported with kernels built with
gcc 2.95 which were solved by compiling it with egcs 2.91.66. So for now please
use version gcc 2.91.66 (aka egcs 1.1.2) to build your XFS kernel.
Also note 2.96 has not been tested its status is unknown at this time.

</P>
<h2>
Q: What are all those other things in the cmd/xfs directory?
</h2>
<p>
Some of them are other interesting tools like: db - <tt>xfs_db</tt> is a xfs
filesystem debugger (working) , copy - <tt>xfs_copy</tt> is tool for 
effectively copying one filesystem to another device (not yet ported), 
fsr - <tt>xfs_fsr</tt> is a defragmenter for xfs (working), 
repair - <tt>xfs_repair</tt> is the consistency checker for an xfs 
filesystem (working).
</p>
<h2>
Q: Why my RedHat 7.0 system does not boot with the XFS beta kernel?
</h2>
<p>
This is because there is a syscall conflict which results in this
problem. Please use the latest XFS code from the cvs tree which has
this fixed. Eventually the beta will be rerolled for that.
</p>
<h2>
Q: My filesystem is ok - but xfs_check or xfs_repair shows errors - whats wrong here?
</h2>
<p>
Don't run those commands on a mounted filesystem - in this case it is
normal that you see inconsistencies. Never run xfs_repair on a mounted
filesystem without the "-n" switch at all. If you ran the commands on
an unmounted filesystem then there seems to be something wrong with
the filesystem.
</P>
<P>

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