- <title>5.2 Determining Space Requirements</title>
- <para>The desired performance characteristics of the backing file systems on the MDT and OSTs are independent of one another. The size of the MDT backing file system depends on the number of inodes needed in the total Lustre file system, while the aggregate OST space depends on the total amount of data stored on the file system.</para>
- <para>Each time a file is created on a Lustre file system, it consumes one inode on the MDT and one inode for each OST object over which the file is striped. Normally, each file's stripe count is based on the system-wide default stripe count. However, this can be changed for individual files using the lfssetstripe option. For more details, see <xref linkend="managingstripingfreespace"/>.</para>
- <para>In a Lustre ldiskfs file system, all the inodes are allocated on the MDT and OSTs when the file system is first formatted. The total number of inodes on a formatted MDT or OST cannot be easily changed, although it is possible to add OSTs with additional space and corresponding inodes. Thus, the number of inodes created at format time should be generous enough to anticipate future expansion.</para>
- <para>When the file system is in use and a file is created, the metadata associated with that file is stored in one of the pre-allocated inodes and does not consume any of the free space used to store file data.</para>
- <note>
- <para>By default, the ldiskfs file system used by Lustre servers to store user-data objects and system data reserves 5% of space that cannot be used by Lustre. Additionally, Lustre reserves up to 400 MB on each OST for journal use and a small amount of space outside the journal to store accounting data for Lustre. This reserved space is unusable for general storage. Thus, at least 400 MB of space is used on each OST before any file object data is saved.<anchor xml:id="dbdoclet.50438256_74070" xreflabel=""/></para>
- </note>
+ <title><indexterm><primary>setup</primary><secondary>space</secondary></indexterm>
+ <indexterm><primary>space</primary><secondary>determining requirements</secondary></indexterm>
+ Determining Space Requirements</title>
+ <para>The desired performance characteristics of the backing file systems
+ on the MDT and OSTs are independent of one another. The size of the MDT
+ backing file system depends on the number of inodes needed in the total
+ Lustre file system, while the aggregate OST space depends on the total
+ amount of data stored on the file system. If MGS data is to be stored
+ on the MDT device (co-located MGT and MDT), add 100 MB to the required
+ size estimate for the MDT.</para>
+ <para>Each time a file is created on a Lustre file system, it consumes
+ one inode on the MDT and one OST object over which the file is striped.
+ Normally, each file's stripe count is based on the system-wide
+ default stripe count. However, this can be changed for individual files
+ using the <literal>lfs setstripe</literal> option. For more details,
+ see <xref linkend="managingstripingfreespace"/>.</para>
+ <para>In a Lustre ldiskfs file system, all the MDT inodes and OST
+ objects are allocated when the file system is first formatted. When
+ the file system is in use and a file is created, metadata associated
+ with that file is stored in one of the pre-allocated inodes and does
+ not consume any of the free space used to store file data. The total
+ number of inodes on a formatted ldiskfs MDT or OST cannot be easily
+ changed. Thus, the number of inodes created at format time should be
+ generous enough to anticipate near term expected usage, with some room
+ for growth without the effort of additional storage.</para>
+ <para>By default, the ldiskfs file system used by Lustre servers to store
+ user-data objects and system data reserves 5% of space that cannot be used
+ by the Lustre file system. Additionally, a Lustre file system reserves up
+ to 400 MB on each OST, and up to 4GB on each MDT for journal use and a
+ small amount of space outside the journal to store accounting data. This
+ reserved space is unusable for general storage. Thus, at least this much
+ space will be used on each OST before any file object data is saved.</para>
+ <para condition="l24">With a ZFS backing filesystem for the MDT or OST,
+ the space allocation for inodes and file data is dynamic, and inodes are
+ allocated as needed. A minimum of 2kB of usable space (before mirroring)
+ is needed for each inode, exclusive of other overhead such as directories,
+ internal log files, extended attributes, ACLs, etc.
+ Since the size of extended attributes and ACLs is highly dependent on
+ kernel versions and site-specific policies, it is best to over-estimate
+ the amount of space needed for the desired number of inodes, and any
+ excess space will be utilized to store more inodes.</para>
+ <section>
+ <title><indexterm>
+ <primary>setup</primary>
+ <secondary>MGT</secondary>
+ </indexterm>
+ <indexterm>
+ <primary>space</primary>
+ <secondary>determining MGT requirements</secondary>
+ </indexterm> Determining MGT Space Requirements</title>
+ <para>Less than 100 MB of space is required for the MGT. The size
+ is determined by the number of servers in the Lustre file system
+ cluster(s) that are managed by the MGS.</para>
+ </section>