+ <section remap="h3">
+ <title><indexterm>
+ <primary>setup</primary>
+ <secondary>limits</secondary>
+ </indexterm><indexterm xmlns:xi="http://www.w3.org/2001/XInclude">
+ <primary>wide striping</primary>
+ </indexterm><indexterm xmlns:xi="http://www.w3.org/2001/XInclude">
+ <primary>xattr</primary>
+ <secondary><emphasis role="italic">See</emphasis> wide striping</secondary>
+ </indexterm><indexterm>
+ <primary>large_xattr</primary>
+ <secondary>ea_inode</secondary>
+ </indexterm><indexterm>
+ <primary>wide striping</primary>
+ <secondary>large_xattr</secondary>
+ <tertiary>ea_inode</tertiary>
+ </indexterm>File and File System Limits</title>
+
+ <para><xref linkend="settinguplustresystem.tab2"/> describes
+ current known limits of Lustre. These limits are imposed by either
+ the Lustre architecture or the Linux virtual file system (VFS) and
+ virtual memory subsystems. In a few cases, a limit is defined within
+ the code and can be changed by re-compiling the Lustre software.
+ Instructions to install from source code are beyond the scope of this
+ document, and can be found elsewhere online. In these cases, the
+ indicated limit was used for testing of the Lustre software. </para>
+
+ <table frame="all" xml:id="settinguplustresystem.tab2">
+ <title>File and file system limits</title>
+ <tgroup cols="3">
+ <colspec colname="c1" colwidth="3*"/>
+ <colspec colname="c2" colwidth="2*"/>
+ <colspec colname="c3" colwidth="4*"/>
+ <thead>
+ <row>
+ <entry>
+ <para><emphasis role="bold">Limit</emphasis></para>
+ </entry>
+ <entry>
+ <para><emphasis role="bold">Value</emphasis></para>
+ </entry>
+ <entry>
+ <para><emphasis role="bold">Description</emphasis></para>
+ </entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>
+ <para>Maximum number of MDTs</para>
+ </entry>
+ <entry>
+ <para condition='l24'>256</para>
+ </entry>
+ <entry>
+ <para>The Lustre software release 2.3 and earlier allows a
+ maximum of 1 MDT per file system, but a single MDS can host
+ multiple MDTs, each one for a separate file system.</para>
+ <para condition="l24">The Lustre software release 2.4 and later
+ requires one MDT for the filesystem root. At least 255 more
+ MDTs can be added to the filesystem and attached into
+ the namespace with DNE remote or striped directories.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum number of OSTs</para>
+ </entry>
+ <entry>
+ <para>8150</para>
+ </entry>
+ <entry>
+ <para>The maximum number of OSTs is a constant that can be
+ changed at compile time. Lustre file systems with up to
+ 4000 OSTs have been tested. Multiple OST file systems can
+ be configured on a single OSS node.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum OST size</para>
+ </entry>
+ <entry>
+ <para>256TiB (ldiskfs), 256TiB (ZFS)</para>
+ </entry>
+ <entry>
+ <para>This is not a <emphasis>hard</emphasis> limit. Larger
+ OSTs are possible but most production systems do not
+ typically go beyond the stated limit per OST because Lustre
+ can add capacity and performance with additional OSTs, and
+ having more OSTs improves aggregate I/O performance,
+ minimizes contention, and allows parallel recovery (e2fsck
+ for ldiskfs OSTs, scrub for ZFS OSTs).
+ </para>
+ <para>
+ With 32-bit kernels, due to page cache limits, 16TB is the
+ maximum block device size, which in turn applies to the
+ size of OST. It is strongly recommended to run Lustre
+ clients and servers with 64-bit kernels.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum number of clients</para>
+ </entry>
+ <entry>
+ <para>131072</para>
+ </entry>
+ <entry>
+ <para>The maximum number of clients is a constant that can
+ be changed at compile time. Up to 30000 clients have been
+ used in production accessing a single filesystem.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum size of a single file system</para>
+ </entry>
+ <entry>
+ <para>at least 1EiB</para>
+ </entry>
+ <entry>
+ <para>Each OST can have a file system up to the
+ Maximum OST size limit, and the Maximum number of OSTs
+ can be combined into a single filesystem.
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum stripe count</para>
+ </entry>
+ <entry>
+ <para>2000</para>
+ </entry>
+ <entry>
+ <para>This limit is imposed by the size of the layout that
+ needs to be stored on disk and sent in RPC requests, but is
+ not a hard limit of the protocol. The number of OSTs in the
+ filesystem can exceed the stripe count, but this limits the
+ number of OSTs across which a single file can be striped.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum stripe size</para>
+ </entry>
+ <entry>
+ <para>< 4 GiB</para>
+ </entry>
+ <entry>
+ <para>The amount of data written to each object before moving
+ on to next object.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Minimum stripe size</para>
+ </entry>
+ <entry>
+ <para>64 KiB</para>
+ </entry>
+ <entry>
+ <para>Due to the use of 64 KiB PAGE_SIZE on some CPU
+ architectures such as ARM and POWER, the minimum stripe
+ size is 64 KiB so that a single page is not split over
+ multiple servers.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum object size</para>
+ </entry>
+ <entry>
+ <para>16TiB (ldiskfs), 256TiB (ZFS)</para>
+ </entry>
+ <entry>
+ <para>The amount of data that can be stored in a single object.
+ An object corresponds to a stripe. The ldiskfs limit of 16 TB
+ for a single object applies. For ZFS the limit is the size of
+ the underlying OST. Files can consist of up to 2000 stripes,
+ each stripe can be up to the maximum object size. </para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum <anchor xml:id="dbdoclet.50438256_marker-1290761" xreflabel=""/>file size</para>
+ </entry>
+ <entry>
+ <para>16 TiB on 32-bit systems</para>
+ <para> </para>
+ <para>31.25 PiB on 64-bit ldiskfs systems,
+ 8EiB on 64-bit ZFS systems</para>
+ </entry>
+ <entry>
+ <para>Individual files have a hard limit of nearly 16 TiB on
+ 32-bit systems imposed by the kernel memory subsystem. On
+ 64-bit systems this limit does not exist. Hence, files can
+ be 2^63 bits (8EiB) in size if the backing filesystem can
+ support large enough objects.</para>
+ <para>A single file can have a maximum of 2000 stripes, which
+ gives an upper single file limit of 31.25 PiB for 64-bit
+ ldiskfs systems. The actual amount of data that can be stored
+ in a file depends upon the amount of free space in each OST
+ on which the file is striped.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum number of files or subdirectories in a single directory</para>
+ </entry>
+ <entry>
+ <para>10 million files (ldiskfs), 2^48 (ZFS)</para>
+ </entry>
+ <entry>
+ <para>The Lustre software uses the ldiskfs hashed directory
+ code, which has a limit of about 10 million files, depending
+ on the length of the file name. The limit on subdirectories
+ is the same as the limit on regular files.</para>
+ <note condition='l28'><para>Starting in the 2.8 release it is
+ possible to exceed this limit by striping a single directory
+ over multiple MDTs with the <literal>lfs mkdir -c</literal>
+ command, which increases the single directory limit by a
+ factor of the number of directory stripes used.</para></note>
+ <para>Lustre file systems are tested with ten million files
+ in a single directory.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum number of files in the file system</para>
+ </entry>
+ <entry>
+ <para>4 billion (ldiskfs), 256 trillion (ZFS)</para>
+ <para condition='l24'>up to 256 times the per-MDT limit</para>
+ </entry>
+ <entry>
+ <para>The ldiskfs filesystem imposes an upper limit of
+ 4 billion inodes per filesystem. By default, the MDT
+ filesystem is formatted with one inode per 2KB of space,
+ meaning 512 million inodes per TiB of MDT space. This can be
+ increased initially at the time of MDT filesystem creation.
+ For more information, see
+ <xref linkend="settinguplustresystem"/>.</para>
+ <para condition="l24">The ZFS filesystem dynamically allocates
+ inodes and does not have a fixed ratio of inodes per unit of MDT
+ space, but consumes approximately 4KiB of mirrored space per
+ inode, depending on the configuration.</para>
+ <para condition="l24">Each additional MDT can hold up to the
+ above maximum number of additional files, depending on
+ available space and the distribution directories and files
+ in the filesystem.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum length of a filename</para>
+ </entry>
+ <entry>
+ <para>255 bytes (filename)</para>
+ </entry>
+ <entry>
+ <para>This limit is 255 bytes for a single filename, the
+ same as the limit in the underlying filesystems.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum length of a pathname</para>
+ </entry>
+ <entry>
+ <para>4096 bytes (pathname)</para>
+ </entry>
+ <entry>
+ <para>The Linux VFS imposes a full pathname length of 4096 bytes.</para>
+ </entry>
+ </row>
+ <row>
+ <entry>
+ <para>Maximum number of open files for a Lustre file system</para>
+ </entry>
+ <entry>
+ <para>No limit</para>
+ </entry>
+ <entry>
+ <para>The Lustre software does not impose a maximum for the number
+ of open files, but the practical limit depends on the amount of
+ RAM on the MDS. No "tables" for open files exist on the
+ MDS, as they are only linked in a list to a given client's
+ export. Each client process probably has a limit of several
+ thousands of open files which depends on the ulimit.</para>
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ <para> </para>
+ <note><para>By default for ldiskfs MDTs the maximum stripe count for a
+ <emphasis>single file</emphasis> is limited to 160 OSTs. In order to
+ increase the maximum file stripe count, use
+ <literal>--mkfsoptions="-O ea_inode"</literal> when formatting the MDT,
+ or use <literal>tune2fs -O ea_inode</literal> to enable it after the
+ MDT has been formatted.</para>
+ </note>
+ </section>