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<h2>
<b><font face="ARIAL NARROW,HELVETICA">XFS for Linux Features</font></b></h2>

<p>
XFS combines advanced journaling technology with full 64-bit addressing and
scalable structures and algorithms.  This combination delivers the most
scalable and high-performance filesystem in the world.
</p>

<h2>
XFS Features
</h2>
<p>
The XFS Filesystem provides the following major features:
<br>
<br>

<ul>
<li>
<b>Journaling: Quick Recovery </b>

<br>
<br>
The XFS journaling technology allows it to restart very quickly
after an unexpected interruption, regardless of the number of files it is
managing.  Traditional filesystems must do special filesystem checks after
an interruption, which can take many hours to complete.  The XFS journaling
avoids these lengthy filesystem checks.
</p>
</li>

<li>
<b>Fast Transactions</b>
<p>
The XFS filesystem provides the advantages of journaling while
minimizing the performance impact of journaling on read and write
data transactions.  Its journaling structures and algorithms
are tuned to log the transactions rapidly.
</p>

<p>
XFS uses efficient table structures for fast searches and rapid space
allocation.  XFS continues to deliver rapid response times, even for
directories with tens of thousands of entries.
</p>
</li>

<li>
<b>High Scalability</b>

<p>
XFS is a full 64-bit filesystem, and thus, as a filesystem,
is capable of handling files as large as a
million terabytes.

<pre>2<sup>63</sup>  = 9 x 10<sup>18</sup> = 9 exabytes </pre>
</p>

<p>
In future, as the filesystem size limitations of Linux are eliminated
XFS will scale to the largest filesystems
</p>

<p>
A million terabytes is about
a million times larger than most large filesystems in use today.
This may seem to be an extremely large address space, but it
is needed to plan for the exponential disk-density
improvements observed in the disk industry in recent years.
As the disk sizes grow, not only does the address space need to be
sufficiently large, but the structures and algorithms need to scale. XFS is
ready today with the technologies needed for this scalability.
</p>
</li>

<li>
<b>Excellent Bandwidth</b>
<p>
XFS as a filesystem is capable of delivering near-raw I/O performance.
XFS has proven scalability on SGI MIPS systems of multiple gigabytes/sec
on multiple terabyte filesystems.  As the bandwidth capabilities of Linux
improve, the XFS filesystem will be able to utilize those capabilities.
</p>
</li>
</ul>
</p>


 
<h2>Technical Specifications</h2>
The technical specification of the XFS filesystem for
Linux are as follows:

<p>
<b>Technology</b>
</p>
<p>
Journaled 64-bit filesystem with guaranteed
filesystem consistency.
</p>

<p>
<b>Product Span</b>
</p>
<p>
Available on Linux 2.4.
</p>

<p>
<b>Quotas</b>
</p>
<p>
The Linux XFS filesystem supports both user and group quotas.
</p>


<p>
<b>Extended Attributes</b>
</p>
<p>
XFS implements fully journaled extended attributes. An extended attribute
is a name/value pair associated with a file. Attributes can be attached to 
all types of inodes:  regular files, directories, symbolic links, 
device nodes, and so forth. Attribute values can contain upto 64KB of 
arbitrary binary data. XFS implements two attribute namespaces: a user
namespace available to all users, protected by the normal file 
permissions; and a system namespace, accessible only to privileged
users. The system namespace can be used for protected filesystem meta-data 
such as access control lists (ACLs) and hierarchical storage manager
(HSM) file migration status.
</p>

<p>
<b>POSIX Access Control Lists (ACLs)</b> 
</p>
<p>
The Linux XFS filesystem supports the ACL semantics and 
interfaces described in the draft POSIX 1003.1e standard. 
</p>


<p>
<b>Maximum File Size</b> 
</p>
<p>
For Linux 2.4, the maximum accessible file offset is 16TB on 4K page size
and 64TB on 16K page size. As Linux moves to 64 bit on block
devices layer, file size limit will increase to 9 million terabytes (or the
system drive limits).
</p>

<p>
<b>Maximum Filesystem Size</b> 
</p>
<p>
For Linux 2.4, 2 TB. As Linux moves to 64 bit on block devices layer,
filesystem limits will increase.
</p>

<p>
<b>Filesystem Block Size</b>
</p>
<p>
Currently fixed at the system page size - 4K on IA32. Filesystem
extents (contiguous data) are configurable at file creation time using
fcntl and are multiples of the filesystem block size.  Single extents
can be up to 4 GB in size.

</p>

<p>
<b>Physical Disk Sector Size Supported</b>
</p>
<p>
512 bytes 
</p>

<p>
<b>NFS Compatibility </b>
</p>
<p>
With NFS version 3, 64-bit filesystems can be exported to other systems that
support the NFS V3 protocol. Systems that use NFS V2 protocol may access XFS
filesystems within the 32-bit limit imposed by the protocol.
</p>

<p>
<b>Windows NT Compatibility</b>
</p>
<p>
SGI uses the Open Source Samba server to export XFS filesystems to Windows
and Windows NT systems. Samba speaks the SMB (Server Message Block) and CIFS
(Common Internet File System) protocols.
</p>

<p>
<b>Backup/Restore</b>
</p>
<p>
xfsdump and xfsrestore can be used for backup and restore of XFS file
systems to local/remote SCSI tapes or files. It supports dumping of extended
attributes and quota information. As the xfsdump format has been preserved
on Linux, XFS dumps created on either IRIX or Linux can be restored onto an
XFS filesystem on either operating system.
</p>

<p>
<b>Support for Hierarchical Storage</b>
</p>
<p>
The Data Management API (DMAPI/XDSM) allows implementation of hierarchical
storage management software with no kernel modifications as well as
high-performance dump programs without requiring "raw" access to the disk
and knowledge of filesystem structures. 
</p>

<p>
<b>Swap to Files</b>
</p>
<p>
Swap to files is supported.
</p>

<p>
<b>Memory</b>
</p>
<p>
64 MB recommended.
</p>


<br>


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