Storage Foundation Cluster File System High Availability 8.0.2 Administrator's Guide - Linux

Access Control Lists

An Access Control List (ACL) stores a series of entries that identify specific users or groups and their access privileges for a directory or file. A file may have its own ACL or may share an ACL with other files. ACLs have the advantage of specifying detailed access permissions for multiple users and groups.

On Linux, ACLs are supported on cluster file systems.

This feature is supported in SFCFSHA.

See the getfacl(1) and setfacl(1) manual pages.

Cache advisories

Cache advisories are set with the mount command on individual file systems, but are not propagated to other nodes of a cluster.

Caching advisories are not set only with the mount command. Caching advisories can be set on per file basis (using VX_SETCACHE ioctl).

See About Veritas File System I/O.

Commands that depend on file access times

File access times may appear different across nodes because the atime file attribute is not closely synchronized in a cluster file system. So utilities that depend on checking access times may not function reliably.

Cross-platform data sharing

Cross-platform data sharing (CDS) allows data to be serially shared among heterogeneous systems where each system has direct access to the physical devices that hold the data. This feature can be used only in conjunction with Veritas Volume Manager (VxVM).

This feature is supported in SFCFSHA.

See the Veritas InfoScale Solutions Guide.

Data deduplication

You can perform post-process periodic deduplication in a file system to eliminate duplicate data without any continuous cost. You can verify whether data is duplicated on demand, and then efficiently and securely eliminate the duplicates. This feature is available with both Veritas InfoScale Storage and Veritas InfoScale Enterprise licenses.

This feature is supported in SFCFSHA.

See About deduplicating data.

Defragmentation

You can perform defragmentation to remove unused space from directories, make all small files contiguous, and consolidate free blocks for file system use.

This feature is supported in SFCFSHA.

See About defragmentation.

Enhanced data integrity modes

VxFS has the following mount command options to enable the enhanced data integrity modes:

This feature is supported in SFCFSHA.

Enhanced performance mode

The default VxFS logging mode, mount -o delaylog, increases performance by delaying the logging of some structural changes. However, delaylog does not provide the equivalent data integrity as the enhanced data integrity modes because recent changes may be lost during a system failure. This option provides at least the same level of data accuracy that traditional UNIX file systems provide for system failures, along with fast file system recovery.

See the mount_vxfs(1M) manual page.

See delaylog mount option.

Enhanced security

RHEL provides user-level security functionalities and features for file systems. These security functionalities can be availed if you enable SELinux at the OS-level.

See the mount_vxfs(1M) manual page.

Extent attributes

VxFS allocates disk space to files in groups of one or more adjacent blocks called extents. VxFS defines an application interface that allows programs to control various aspects of the extent allocation for a given file. The extent allocation policies associated with a file are referred to as extent attributes.

This feature is supported in SFCFSHA.

See About extent attributes.

Extent-based allocation

An extent is a contiguous area of storage in a computer file system, reserved for a file. When starting to write to a file, a whole extent is allocated. When writing to the file again, the data continues where the previous write left off. This reduces or eliminates file fragmentation. An extent is presented as an address-length pair, which identifies the starting block address and the length of the extent (in file system or logical blocks). Since VxFS is an extent-based file system, addressing is done through extents (which can consist of multiple blocks) rather than in single-block segments. Extents can therefore enhance file system throughput.

This feature is supported in SFCFSHA.

See About extents.

Extended mount options

This feature is supported in SFCFSHA.

See Mounting a VxFS file system.

Fast file system recovery

Most file systems rely on full structural verification by the fsck utility as the only means to recover from a system failure. For large disk configurations, this involves a time-consuming process of checking the entire structure, verifying that the file system is intact, and correcting any inconsistencies. VxFS provides fast recovery with the VxFS intent log and VxFS intent log resizing features.

This feature is supported in SFCFSHA.

See About the Veritas File System intent log.

File Change Log

The VxFS File Change Log (FCL) tracks changes to files and directories in a file system. The File Change Log can be used by applications such as backup products, webcrawlers, search and indexing engines, and replication software that typically scan an entire file system searching for modifications since a previous scan. FCL functionality is available on all the four Veritas InfoScale licenses: Veritas InfoScale™ Storage, Veritas InfoScale™ Availability, Veritas InfoScale™ Foundation, and Veritas InfoScale™ Enterprise .

This feature is supported in SFCFSHA.

See About Veritas File System File Change Log.

File compression

Compressing files reduces the space used by files, while retaining the accessibility of the files and being transparent to applications. Compressed files look and behave almost exactly like uncompressed files: the compressed files have the same name, and can be read and written as with uncompressed files. Reads cause data to be uncompressed in memory, only; the on-disk copy of the file remains compressed. In contrast, after a write, the new data is uncompressed on disk.

This feature is supported in SFCFSHA.

See About compressing files.

File replication

You can perform cost-effective periodic replication of data over IP networks, giving organizations an extremely flexibile storage independent data availability solution for disaster recovery and off-host processing.

This feature is supported in SFCFSHA.

See the Veritas InfoScale Replication Administrator's Guide..

File system snapshots

VxFS provides online data backup using the snapshot feature. An image of a mounted file system instantly becomes an exact read-only copy of the file system at a specific point in time. The original file system is called the snapped file system, while the copy is called the snapshot.

When changes are made to the snapped file system, the old data is copied to the snapshot. When the snapshot is read, data that has not changed is read from the snapped file system, changed data is read from the snapshot.

This feature is supported in SFCFSHA.

See About snapshot file systems.

FileSnaps

A FileSnap is a space-optimized copy of a file in the same name space, stored in the same file system. VxFS supports FileSnaps on file systems with disk layout Version 8 or later.

This feature is supported in SFCFSHA.

See About FileSnaps.

Freezing and thawing file systems

Freezing a file system is a necessary step for obtaining a stable and consistent image of the file system at the volume level. Consistent volume-level file system images can be obtained and used with a file system snapshot tool.

This feature is supported in SFCFSHA. Synchronizing operations, which require freezing and thawing file systems, are done on a cluster-wide basis.

See Freezing and thawing a file system.

Improved synchronous writes

VxFS provides superior performance for synchronous write applications. The mount -o datainlog option greatly improves the performance of small synchronous writes.

The mount -o convosync=dsync option improves the performance of applications that require synchronous data writes but not synchronous inode time updates.

See the mount_vxfs(1M) manual page.

See convosync mount option.

Locking

For the F_GETLK command, if there is a process holding a conflicting lock, the l_pid field returns the process ID of the process holding the conflicting lock. The nodeid-to-node name translation can be done by examining the /etc/llthosts file or with the fsclustadm command.

This feature is supported in SFCFSHA except for mandatory locking, and deadlock detection supported by traditional fcntl locks.

See the fcntl(2) manual page.

maxlink support

Added support for more than 64K sub-directories. If maxlink is disabled on a file system, the sub-directory limit will be 32K by default. If maxlink is enabled on a file system, this allows you to create up to 4294967295(2^32 - 1) sub-directories.

By default maxlink is enabled.

To enable the maxlink option at mkfs time. For example:

# mkfs -t vxfs -o maxlink /dev/vx/rdsk/testdg/vol1

To disable the maxlink option at mkfs time. For example:

# mkfs -t vxfs -o nomaxlink /dev/vx/rdsk/testdg/vol1

To enable the maxlink option through the fsadm command on a mounted files system. For example:

# fsadm -t vxfs -o maxlink /mnt1

To disable the maxlink option through the fsadm command on a mounted file system. For example:

# fsadm -t vxfs -o nomaxlink /mnt1

See the mkfs_vxfs(1M) and fsadm_vxfs(1M) manual pages.

Memory mapping

You can use the mmap() function to establish shared memory mapping.

This feature is supported in SFCFSHA.

See the mmap(2) manual page.

Multi-volume file systems

The multi-volume file system (MVFS) feature allows several volumes to be represented by a single logical object. All I/O to and from an underlying logical volume is directed by way of volume sets. You can create a single VxFS file system on this multi-volume set. This feature can be used only in conjunction with VxVM. MVFS functionality is available on all the four Veritas InfoScale licenses: Veritas InfoScale™ Storage, Veritas InfoScale™ Availability, Veritas InfoScale™ Foundation, and Veritas InfoScale™ Enterprise.

See About multi-volume file systems.

Nested Mounts

You can use a directory on a cluster mounted or local mounted file system as a mount point for a local file system or another cluster file system.

This feature is supported in SFCFSHA.

NFS mounts

You export the NFS file systems from the cluster. You can NFS export CFS file systems in a distributed highly available way.

This feature is supported in SFCFSHA.

Partitioned directories

Parallel threads that access a large volume and perform access and updates on a directory that commonly exist in a file system, suffer from an exponentially longer wait time for the threads.

This feature creates partitioned directories to improve the directory performance of file systems. When any directory crosses the tunable threshold, this feature takes an exclusive lock on the directory inode and redistributes the entries into various respective hash directories. These hash directories are not visible in the name-space view of the user or operating system. For every new create, delete, or lookup thread, this feature performs a lookup for the respective hashed directory (depending on the target name) and performs the operation in that directory. This leaves the parent directory inode and its other hash directories unobstructed for access, which vastly improves file system performance.

This feature operates only on disk layout Version 8 or later file systems.

This feature is supported in SFCFSHA.

See Partitioned directories.

See the vxtunefs(1M) and fsadm_vxfs(1M) manual pages.

Quotas

VxFS supports quotas, which allocate per-user and per-group quotas and limit the use of two principal resources: files and data blocks. You can assign quotas for each of these resources. Each quota consists of two limits for each resource: hard limit and soft limit.

The hard limit represents an absolute limit on data blocks or files. A user can never exceed the hard limit under any circumstances.

The soft limit is lower than the hard limit and can be exceeded for a limited amount of time. This allows users to exceed limits temporarily as long as they fall under those limits before the allotted time expires.

This feature is supported in SFCFSHA.

See About Veritas File System quota limits.

Reverse path name lookup

The reverse path name lookup feature obtains the full path name of a file or directory from the inode number of that file or directory. The reverse path name lookup feature can be useful for a variety of applications, such as for clients of the VxFS File Change Log feature, in backup and restore utilities, and for replication products. Typically, these applications store information by inode numbers because a path name for a file or directory can be very long, thus the need for an easy method of obtaining a path name.

This feature is supported in SFCFSHA.

See About reverse path name lookup.

SmartIO

The SmartIO feature of Storage Foundation and High Availability Solutions (SFHA Solutions) enables data efficiency on SSDs or other supported devices through I/O caching. Using SmartIO to improve efficiency, you can optimize the cost per IOPS. SmartIO uses advanced, customizable heuristics to determine what data to cache and how that data gets removed from the cache. The heuristics take advantage of SFHA Solutions' knowledge of the characteristics of the workload.

SmartIO uses a cache area on the target device or devices. The cache area is the storage space that SmartIO uses to store the cached data and the metadata about the cached data. The type of the cache area determines whether it supports VxFS caching or VxVM caching.

This feature is supported in SFCFSHA.

See the Veritas InfoScale SmartIO for Solid State Drives Solutions Guide.

SmartTier

The SmartTier option is built on a multi-volume file system. Using SmartTier, you can map more than one volume to a single file system. You can then configure policies that automatically relocate files from one volume to another, or relocate files by running file relocation commands. Having multiple volumes lets you determine where files are located, which can improve performance for applications that access specific types of files. SmartTier functionality is available with both Veritas InfoScale Storage and Veritas InfoScale Enterprise licenses.

This feature is supported in SFCFSHA.

See About SmartTier.

Storage Checkpoints

To increase availability, recoverability, and performance, VxFS offers on-disk and online backup and restore capabilities that facilitate frequent and efficient backup strategies. Backup and restore applications can leverage a Storage Checkpoint, a disk- and I/O-efficient copying technology for creating periodic frozen images of a file system. Storage Checkpoints present a view of a file system at a point in time, and subsequently identifies and maintains copies of the original file system blocks. Instead of using a disk-based mirroring method, Storage Checkpoints save disk space and significantly reduce I/O overhead by using the free space pool available to a file system.

Storage Checkpoint functionality is available with both Veritas InfoScale Storage and Veritas InfoScale Enterprise licenses.

This feature is supported in SFCFSHA.

See About Storage Checkpoints.

Support for large files and large file systems

VxFS supports files larger than two gigabytes and large file systems up to 256 terabytes.

See largefiles and nolargefiles mount options.

Swap files

Swap files are not supported on cluster-mounted file systems.

Temporary file system mode

On most UNIX systems, temporary file system directories, such as /tmp and /usr/tmp, often hold files that do not need to be retained when the system reboots. The underlying file system does not need to maintain a high degree of structural integrity for these temporary directories. VxFS provides the mount -o tmplog option, which allows the user to achieve higher performance on temporary file systems by delaying the logging of most operations.

See the mount_vxfs(1M) manual page.

See tmplog mount option.

Thin Reclamation

The Thin Reclamation feature allows you to release free data blocks of a VxFS file system to the free storage pool of a Thin Storage LUN. This feature is only supported on file systems created on a VxVM volume.