fsadm_vxfs(1M)

Options

fsadm recognizes the following options:

If no options are specified, fsadm prints the current largefiles flag setting, then exits. The -b, -o largefiles, and -o nolargefiles options cannot be specified if any other options are given. If both -e and -d are specified, fsadm first completes the directory reorganization, then does the extent reorganization.

Operands

fsadm recognizes the following operands:

Largefiles Flag

Files larger than two gigabytes are called large files. The -o largefiles and -o nolargefiles options change the largefiles flag, allowing or disallowing large files in the file system.

Large files can be created only on file systems with disk layout Version 3 or above. A file system with large files cannot be mounted on an HP-UX system older than HP-UX 10.20. Many existing applications cannot operate on large files.

Setting the flag with the -o largefiles option succeeds only if the file system has the Version 3 disk layout or above. See vxupgrade(1M) for information on how to upgrade a file system from an older disk layout to the current version. Clearing the flag with the -o nolargefiles option succeeds only if the flag is set and there are no large files present on the file system. See mkfs_vxfs(1M) and mount_vxfs(1M) for information on creating and mounting file systems with large files.

The -o largefiles and -o nolargefiles options are the only fsadm options that can be used on an unmounted file system. An unmounted file system can be specified by invoking fsadm with a special device rather than a mount point. If an unmounted file system is specified, it must be clean.

Changing the largefiles flag may require changes to /etc/fstab. For example, if fsadm is used to set the largefiles flag, but nolargefiles is specified as a mount option in /etc/fstab, the files system is not mountable.

Defragmentation

For optimal performance, the kernel-extent allocator must be able to find large extents when it wants them. To maintain file-system performance, run fsadm periodically against all VxFS file systems to reduce fragmentation. The frequency depends on file system usage and activity patterns, and the importance of performance; typically between once a day and once a month against each file system. The -v option can be used to examine the amount of work performed by fsadm. You can adjust the frequency of reorganization based on the rate of file system fragmentation.

There are two options that are available to control the amount of work done by fsadm. The -t option specifies a maximum length of time to run. The -p option specifies a maximum number of passes to run. If both are specified, fsadm exits if either of the terminating conditions is reached. By default, fsadm runs 5 passes. If both the -e and -d options are specified, fsadm runs all the directory reorganization passes before any extent reorganization passes.

fsadm uses the file .fsadm in the lost+found directory as a lock file. When fsadm is invoked, it opens the file lost+found/.fsadm in the root of the file system specified by mount_point. If the file does not exist, it is created. The fcntl(2) system call obtains a write lock on the file. If the write lock fails, fsadm assumes that another instance of fsadm is running and fails. fsadm reports the process ID of the process holding the write lock on the .fsadm file.

File System Resizing

If the -b option is specified, fsadm resizes the file system whose mount point is mount_point. If newsize is larger than the current size of the file system, the file system is expanded to newsize sectors. Similarly, if newsize is smaller than the current size of the file system, fsadm shrinks the file system to newsize sectors.

Increasing the size of a file system requires that the file system contain enough free space, prior to the expansion, for the growth of the structural files. In the case where a file system has no free blocks available, the attempt to increase the size of the file system will fail (see extendfs(1M) for an alternate method to increase file system size).

In a Version 3 or above disk layout, if there are file system resources in use in the sectors being removed, fsadm relocates those resources to sectors staying within the resized file system. The time needed for relocation depends on the number of blocks being moved.

In older disk layouts, file system structural components are fixed, so reducing the size of a file system fails if there are file system resources in use in the sectors being removed. In that case, a reorganization (using fsadm -e) can free busy resources and allow shrinking the file system. If there are still file system structural components within the area to be removed, you must upgrade the file system to a Version 3 or above disk layout to do a resize (see vxupgrade(1M)).

Reporting on Directory Fragmentation

As files are allocated and freed, directories tend to grow and become sparse. In general, a directory is as large as the largest number of files it ever contained, even if some files were subsequently removed.

To obtain a directory fragmentation report, use the command syntax:

fsadm -D [-r rawdev] mount_point

The following is some example output from the fsadm -D command:

# fsadm -F vxfs -D /lhome

The column labeled "Dirs Searched" contains the total number of directories. A directory is associated with the extent-allocation unit containing the extent in which the directory's inode is located. The column labeled "Total Blocks" contains the total number of blocks used by directory extents.

The column labeled "Immed Dirs" contains the number of directories that are immediate, meaning that the directory data is in the inode itself, as opposed to being in an extent. Immediate directories save space and speed up pathname resolution. The column labeled "Immeds to Add" contains the number of directories that currently have a data extent, but that could be reduced in size and contained entirely in the inode.

The column labeled "Dirs to Reduce" contains the number of directories for which one or more blocks could be freed if the entries in the directory are compressed to make the free space in the directory contiguous. Since directory entries vary in length, it is possible that some large directories may contain a block or more of total free space, but with the entries arranged in such a way that the space cannot be made contiguous. As a result, it is possible to have a non-zero "Dirs to Reduce" calculation immediately after running a directory reorganization. The -v (verbose) option of directory reorganization reports occurrences of failure to compress free space.

The column labeled "Blocks to Reduce" contains the number of blocks that could be freed if the entries in the directory are compressed.

Measuring Directory Fragmentation

If the totals in the columns labeled "Dirs to Reduce" are substantial, a directory reorganization can improve performance of pathname resolution. The directories that fragment tend to be the directories with the most activity. A small number of fragmented directories may account for a large percentage of name lookups in the file system.

Directory Reorganization

If the -d option is specified, fsadm reorganizes the directories on the file system whose mount point is mount_point. Directories are reorganized in two ways: compression and sorting.

For compression, fsadm moves valid entries to the front of the directory and groups the free space at the end of the directory. If there are no entries in the last block of the directory, the block is released and the directory size is reduced.

If the total space used by all directory entries is small enough, fsadm puts the directory in the inode immediate data area.

fsadm also sorts directory entries to improve pathname lookup performance. Entries are sorted based on the last access time of the entry. The -a option specifies a time interval; 14 days is the default if -a is not specified. The time interval is broken up into 128 buckets, and all times within the same bucket are considered equal. All access times older than the time interval are considered equal, and those entries are placed last. Subdirectory entries are placed at the front of the directory and symbolic links are placed after subdirectories, followed by the most-recently-accessed files.

The command syntax for reorganizing directories in a file system is:

fsadm -d [-D] [-v] [-s] [-a days] [-p passes] [-r rawdev] [-t time] mount_point

The following example shows the output of the fsadm -d -D command:

The column labeled "Dirs Searched" contains the number of directories searched. Only directories with data extents are reorganized. Immediate directories are skipped. The column labeled "Dirs Changed" contains the number of directories for which a change was made.

The column labeled "Total Ioctls" contains the total number of VX_DIRSORT ioctls performed. Reorganization of directory extents is performed using this ioctl.

The column labeled "Failed Ioctls" contains the number of requests that failed for some reason. The reason for failure is usually that the directory being reorganized is active. A few failures should be no cause for alarm. If the -v option is used, all ioctl calls and status returns are recorded.

The column labeled "Blocks Reduced" contains the total number of directory blocks freed by compressing entries. The column labeled "Blocks Changed" contains the total number of directory blocks updated while sorting and compressing entries.

The column labeled "Immeds Added" contains the total number of directories with data extents that were compressed into immediate directories.

Reporting on Extent Fragmentation

As files are created and removed over time, the free extent map for an allocation unit changes from having one large free area to having many smaller free areas. This process is known as fragmentation. Also, when files increase in size (particularly when growth occurs in small increments) small files can be allocated in multiple extents. In the best case, each file that is not sparse would have exactly one extent (containing the entire file), and the free-extent map is one continuous range of free blocks.

Conversely, in a case of extreme fragmentation, there can be free space in the file system, none of which can be allocated. For example, on Version 2 disk layouts, the indirect-address extent size is always 8K long. This means that to allocate an indirect-address extent to a file, an 8K extent must be available. If no extent of 8K byes or larger is available, even though more than 8K of free space is available, an attempt to allocate a file into indirect extents fails and returns ENOSPC.

Determining Fragmentation

To determine whether a file system is fragmented, the free extents for that file system must be examined. If a large number of small extents are free, then there is fragmentation. If more than half of the amount of free space is taken up by small extents (smaller than 64 blocks), or there is less than 5 percent of total file system space available in large extents, then there is serious fragmentation.

Running the Extent-Fragmentation Report

The extent-fragmentation report provides detailed information about the degree of fragmentation in a given file system.

The command syntax for an extent-fragmentation report is:

fsadm -E [-l largesize] [-r rawdev] mount_point

The extent reorganization facility considers some extents to be immovable: that is, if reallocating and consolidating extents does not improve performance, those extents are considered immovable. For example, if a file already contains large extents, reallocating and consolidating these extents does not improve performance. The -l option controls when fsadm considers an extent as immovable. By default, largesize is 64 blocks, meaning that any extent larger than 64 blocks is considered to be immovable. For the extent-fragmentation report, the value for largesize affects which extents are reported as being immovable extents.

The following is an example of the output generated by the fsadm -E command:

The numbers in the column "Total Files" indicate the total number of files that have data extents. The column "Average File Blks" contains the average number of blocks belonging to all files. The column "Average # Extents" contains the average number of extents used by files in the file system. The column "Total Free Blks" contains the total number of free blocks in the file system. The total number of blocks used for indirect address extent are reported as "blocks used for indirects".

The general shape of free extent map is also reported. There are two percentages reported: % free extents smaller than 64 blocks and % free extents smaller than 8 blocks. These numbers are typically near zero on an unfragmented file system.

Another metric reported is the percentage of blocks that are part of extents 64 blocks or larger. Files with a single small extent are not included in this calculation. This number is generally large on file systems that contain many large files, and is small on file systems that contain many small files.

The figures under the heading "Free Extents By Size" indicate the totals for free extents of each size. The totals are for free extents of size 1, 2, 4, 8, 16, ... up to a maximum of the number of data blocks in an allocation unit. The totals are similar to the output of the df -o command unless there was recent allocation or deallocation activity (because fsadm acts on mounted file systems). These figures provide an indication of fragmentation and extent availability on a file system.

Extent Reorganization

If the -e option is specified, fsadm reorganizes the data extents on the file system whose mount point is mount_point. The primary goal of extent reorganization is to defragment the file system.

To reduce fragmentation, extent reorganization tries to place all small files in one contiguous extent. The -l option specifies the size of a file that is considered large. The default is 64 blocks. Extent reorganization also tries to group large files into large extents of at least 64 blocks. Extent reorganization can improve performance. Small files can be read or written in one I/O operation. Large files can approach raw-disk performance for sequential I/O operations.

fsadm performs extent reorganization on all inodes on the file system. Each pass through the inodes will move the file system closer to optimal organization.

fsadm reduces both file fragmentation and free extent fragmentation in each pass. In older versions of VxFS, considerable effort was made to obtain an optimal file system layout. In current versions, fsadm relies on VxFS kernel allocation mechanisms to reallocate files in a more favorable extent geometry. At the same time, the kernel allocation mechanism is prevented from using blocks in areas of the free list that fsadm tries to make more contiguous.

The command syntax to perform extent reorganization is

fsadm -e [-E] [-v] [-s] [-l largesize] [-p passes] [-r rawdev] [-t time] mount_point

The following example shows the output from the fsadm -F vxfs -e -s -E command:

Note that the default five passes were scheduled, but the reorganization finished in two passes.

This file system had a significant amount of free space although there were several free small extents. The situation was corrected by reallocating one or more of the extents on many of the files. The files selected for reallocation in this case are those with extents in the heavily fragmented section of the allocation units. The time it takes to complete extent reorganization varies, depending on the degree of fragmentation, disk speed, and the number of inodes in the file system. In general, extent reorganization takes approximately one minute for every 100 megabytes of disk space.

In the preceding example, the column "Extents Searched" contains the total number of extents examined. The column "Reallocations Attempted" contains the total number of consolidations or merging of extents performed. The column "Ioctls Issued" contains the total number of reorganization request calls made during the pass. This corresponds closely to the number of files that are being operated on in that pass as most files can be reorganized with a single ioctl. (More than one extent may be consolidated in one operation.)

The column "FileBusy" (located under the heading "Errors") shows the total number of reorganization requests that failed because the file was active during reorganization. The column "NoSpace" (located under the heading "Errors") contains the total number of reorganization requests that failed because an extent presumed free was allocated during the reorganization. The column "Total" (located under the heading "Errors") is the total number or errors encountered during the reorganization and may include errors that were not included with "FileBusy" or "NoSpace."

The following command performs an extent reorganization on sll individual files under the mount point /home.