<emphasis role="italic">bytes-per-inode</emphasis> ratio ("inode ratio")
used for OSTs of various sizes when they are formatted.</para>
<para>
- <table frame="all">
- <title xml:id="settinguplustresystem.tab1">Default Inode Ratios
- Used for Newly Formatted OSTs</title>
+ <table frame="all" xml:id="settinguplustresystem.tab1">
+ <title>Default Inode Ratios Used for Newly Formatted OSTs</title>
<tgroup cols="3">
<colspec colname="c1" colwidth="3*"/>
<colspec colname="c2" colwidth="2*"/>
</indexterm>File and File System Limits</title>
<para><xref linkend="settinguplustresystem.tab2"/> describes
- file and file system size limits. These limits are imposed by either
+ 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.
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">
- <title xml:id="settinguplustresystem.tab2">File and file system limits</title>
+ <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*"/>
<para> Maximum number of MDTs</para>
</entry>
<entry>
- <para> 1</para>
- <para condition='l24'>4096</para>
+ <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. Up to 4095 additional MDTs can be added to the file system and attached
- into the namespace with remote directories.</para>
+ <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>
<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.</para>
+ <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>
<para> 128TB (ldiskfs), 256TB (ZFS)</para>
</entry>
<entry>
- <para>This is not a <emphasis>hard</emphasis> limit. Larger OSTs are possible but
- today typical production systems do not go beyond the stated limit per OST. </para>
+ <para>This is not a <emphasis>hard</emphasis> limit. Larger
+ OSTs are possible but today typical 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 and
+ minimizes contention.
+ </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>
<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.</para>
+ <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.</para>
</entry>
</row>
<row>
<para> 512 PB (ldiskfs), 1EB (ZFS)</para>
</entry>
<entry>
- <para>Each OST or MDT on 64-bit kernel servers can have a file system up to the above limit. On 32-bit systems, due to page cache limits, 16TB is the maximum block device size, which in turn applies to the size of OST on 32-bit kernel servers.</para>
- <para>You can have multiple OST file systems on a single OSS node.</para>
+ <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>
<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.</para>
+ <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>
<para> < 4 GB</para>
</entry>
<entry>
- <para>The amount of data written to each object before moving on to next object.</para>
+ <para>The amount of data written to each object before moving
+ on to next object.</para>
</entry>
</row>
<row>
<para> 64 KB</para>
</entry>
<entry>
- <para>Due to the 64 KB PAGE_SIZE on some 64-bit machines, the minimum stripe size is set to 64 KB.</para>
+ <para>Due to the 64 KB PAGE_SIZE on some 64-bit machines,
+ the minimum stripe size is set to 64 KB.</para>
</entry>
</row>
- <row> <entry>
- <para> Maximum object size</para> </entry>
+ <row>
+ <entry>
+ <para> Maximum object size</para>
+ </entry>
<entry>
<para> 16TB (ldiskfs), 256TB (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 contain the maximum object size. </para>
+ <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>
<para> 31.25 PB on 64-bit ldiskfs systems, 8EB on 64-bit ZFS systems</para>
</entry>
<entry>
- <para>Individual files have a hard limit of nearly 16 TB 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 (8EB) 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 PB 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>
+ <para>Individual files have a hard limit of nearly 16 TB 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 (8EB) 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 PB 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>
<para condition="l22">In Lustre software releases prior to version 2.2,
the maximum stripe count for a single file was limited to 160 OSTs.
In version 2.2, the wide striping feature was added to support files
- striped over up to 2000 OSTs. In order to store the layout for
- such large files, the ldiskfs <literal>ea_inode</literal> feature must
- be enabled on the MDT. This feature is disabled by default at
+ striped over up to 2000 OSTs. In order to store the large layout for
+ such files in ldiskfs, the <literal>ea_inode</literal> feature must
+ be enabled on the MDT, but no similar tunable is needed for ZFS MDTs.
+ This feature is disabled by default at
<literal>mkfs.lustre</literal> time. In order to enable this feature,
specify <literal>--mkfsoptions="-O ea_inode"</literal> at MDT format
time, or use <literal>tune2fs -O ea_inode</literal> to enable it after
git://git.whamcloud.com / doc / manual.git / blobdiff