Lustre which ost

For instance, a 3TB file could use a stripe count of For much larger files, a stripe count of -1 is preferred so that the files are striped across all the OSTs. A tar archive can be created and placed within the directory with a large stripe size. The archive will inherit the stripe size of the directory. If a file to be opened is not subject to write s , it should be opened as read-only.

Limit the number of files in a single directory using a directory hierarchy. For large scale applications that are going to write large numbers of files using private data, it is best to implement a subdirectory structure to limit the number of files in a single directory.

A suggested approach is a two-level directory structure with sqrt N directories each containing sqrt N files, where N is the number of tasks. If many processes need the information from stat on a single file, it is most efficient to have a single process perform the stat call, then broadcast the results. The C and Fortran code snippets in Figures 4.

If you will be writing to a file many times throughout the application run, it is more efficient to open the file once at the beginning. Data can then be written to the file during the course of the run. The file can be closed at the end of the application run. This can be done using the command in Figure 4. If you are going to create many small files in a single directory, greater efficiency will be achieved if you have the directory default to 1 OST on creation.

This is especially effective when extracting source code distributions from a tarball as depicted in Figure 4. All of the source files, header files, and other items only span one OST. When you build the code, all of the object files will only use one OST. The binary will span one OST, but it can copied using the commands in Figure 4. Single shared files should have a stripe count equal to the number of processes which access the file.

If the number of processes accessing the file is greater than then the stripe count should be set to -1 max The stripe size should be set to allow as much stripe alignment as possible. A single process should not need to access stripes on all utilized OSTs. Set the stripe count appropriately for applications which utilize a file-per-process.

At large scales, even when a stripe count of 1 is utilized, it is very possible that OST contention will adversely affect performance. The most effective implementation is to set the stripe count on a directory to 1 and write all files within this directory. Instead of reading a small file from every task, it is advisable to read the entire file from one task and broadcast the contents to all other tasks.

In addition, you will get better performance by making these stripe aligned, where possible. Limit output to these streams to one process in production jobs.

Debugging messages which originate from each process should be disabled in production runs. Frequent buffer flushes on these streams should be avoided.

This action will limit the number of files File-per-process or limit the number of processes accessing file system resources Single-shared-file. Recognize situations where file system contention may limit performance. Main Menu Main Menu. User file data is stored in one or more objects, with each object stored on a separate OST.

The number of objects per file is user configurable and can be tuned to optimize performance for a given workload. Storing the metadata on a MDT provides an efficient division of labor between computing and storage resources. Each file on the MDT contains the layout of the associated data file, including the OST number and object identifier and points to one or more objects associated with the data file.

File Striping Basics A key feature of the Lustre file system is its ability to distribute the segments of a single file across multiple OSTs using a technique called file striping. Aligned Stripes In Figure 1. Non-Aligned Stripes Next, we give an example where the stripes are not aligned. Process 0 writes 0. Figure 2. File-per-Process File-per-process is a communication pattern in which each process of a parallel application writes its data to a private file.

Improved performance can be obtained from a parallel file system such as Lustre. For all options to format backing ldiskfs filesystems, see the mke2fs 8 man page; this section only discusses some Lustre-specific options. For ZFS filesystems, see the zpool 8 man page. You should not specify the -i option with an inode ratio below one inode per bytes in order to avoid problems running out of space on the MDT before all of the inodes are allocated.

Instead, use the -N option. Lustre uses "large" inodes on the backing file systems in order to efficiently store Lustre metadata with each file. Lustre or more specifically the backing ldiskfs file system , also needs sufficient space left for other metadata like the journal up to 4GB , bitmaps and directories.

There are also a few regular files that Lustre uses to maintain cluster consistency. We do NOT recommend specifying a smaller-than-default inode size, as this can lead to serious performance problems; and you cannot change this parameter after formatting the file system.

The inode ratio must always be larger than the inode size. For OST file systems, it is normally advantageous to take local file system usage into account. Try and minimize the number of inodes created on each OST, while keeping enough margin for potential variance in future usage. This helps in reducing the format and e2fsck time, and makes more space available for data. The current default is to create one inode per 64KB of space in the OST file system, but in many environments, this is far too many inodes for the average file size.

The df output in the example below shows a more balanced system compared to the df output in the example in Handling Full OSTs. Updated: Mar Contents. Navigation menu Personal tools Log in Request account. Namespaces Page Discussion.

As an analogy, one can think of the objects of a file as virtual equivalents of disk drives in a RAID-0 storage array. Data is written in fixed-sized chunks in stripes across the objects.

The stripe width is also configurable when the file is created, and defaults to 1MiB to match the default RPC size. Figure 1 shows some examples of file with different storage layouts. The number of objects and the size of the stripe is configurable when the file is created.

Each object grows in size as data is written to it, and may be sparse have holes if the file is not written contiguously by the application. The object blocksize unit of OST space allocation is independent of the Lustre stripe size unit of data distribution across OSTs for the file. The object layout specification for a file can be supplied explicitly by the user via lfs 1 or application, otherwise it will be assigned by the MDT based on either the file system default layout, or by a layout policy defined for the directory in which the file has been created.

The MDS is responsible for the assignment of objects to a file. Objects for a file are normally allocated when the file is created although for efficiency, the MDT will pre-create a pool of zero-length objects on the OSTs, ready for assignment to files as they are created. Objects are initially empty when created and all objects for a file or the first component of a PFL file are created when the file itself is created.