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|Sun QFS File System 5.3 Configuration and Administration Guide Sun QFS and Sun Storage Archive Manager 5.3 Information Library|
Key features of the Sun QFS file systems are described in the following sections:
Sun QFS file systems support both striped and round-robin disk access. The master configuration file (mcf) and the mount parameters specify the volume management features and enable the file system to recognize the relationships between the devices it controls. This feature is in contrast to most UNIX file systems, which can address only one device or one portion of a device. Sun QFS file systems do not require additional volume management applications. However, if you want to use mirroring for devices in a Sun QFS environment, you must obtain an additional package, such as a logical volume manager.
The Sun QFS integrated volume management features use the standard Oracle Solaris OS device driver interface to pass I/O requests to and from the underlying devices. The Sun QFS software groups storage devices into family sets upon which each file system resides.
The Sun QFS file system supports two different types of I/O:
Paged I/O (also known as cached or buffered I/O) – When paged I/O is used, user data is cached in virtual memory pages and the kernel writes the data to disk. The standard Oracle Solaris OS interfaces manage paged I/O. This is the default type of I/O for Sun QFS .
Direct I/O – When direct I/O is used, user data is written directly from user memory to disk. You can specify direct I/O by using the Oracle Solaris OS directio(3C) function call or the setfa command with the -D option. By using direct I/O, you can realize substantial performance improvements for large block, sequential, aligned I/O.
The Sun QFS software supports files of up to 2 63 bytes in length. Very large files can be striped across many disks or RAID devices, even within a single file system, because Sun QFS file systems use true 64-bit addressing. In contrast, standard UNIX file systems are not true 64-bit file systems.
The number of file systems that you can configure is virtually unlimited. The volume manager enables each file system to include up to 252 device partitions, typically disk partitions. Each partition can include up to 16 terabytes of data. This configuration offers virtually unlimited storage capacity.
There is no predefined limit on the number of files in a Sun QFS file system. Because the inode space (which holds information about the files) is dynamically allocated, the maximum number of files is limited only by the amount of disk storage available. The inodes are cataloged in the .inodes file under the mount point. The .inodes file requires a minimum of 512 bytes of storage per file.
In a Sun QFS file system, the inodes are located on the metadata devices and can be separated from the file data devices. In practice, the size of your metadata (mm) devices limits the number of files in a Sun QFS file system, but you can increase the maximum number of files by adding more metadata devices. The hard limit on the number of files is 2 32 -1 files, and the recommended limit is 108 files.
A key function of a file system is its ability to recover quickly after an unscheduled outage. Standard UNIX file systems require a lengthy file system check, fsck, to repair inconsistencies after a system failure.
A Sun QFS file system often does not require a file system check after a disruption that prevents the file system from being written to disk using the sync command. In addition, Sun QFS file systems recover from system failures without using journaling. They recover dynamically by using identification records, serial writes, and error checking for all critical I/O operations. After a system failure, even multiterabyte-sized Sun QFS file systems can be remounted immediately.
File systems use metadata to reference file and directory information. Typically, metadata resides on the same device as the file data. However, the Sun QFS file system has the option of separating the file system metadata from the file data by storing them on separate devices. The Sun QFS file system enables you to define one or more separate metadata devices in order to reduce device head movement and rotational latency, improve RAID cache utilization, or mirror metadata without mirroring file data.
Sun QFS file systems store inode metadata information in a separate file. This practice enables the number of files, and the file system as a whole, to be enlarged dynamically.
The Sun QFS file system is implemented through the standard Oracle Solaris OS virtual file system (vfs/vnode) interface.
By using the vfs/vnode interface, the file system works with the standard Oracle Solaris OS kernel and requires no modifications to the kernel for file management support. Thus, the file system is protected from operating system changes and typically does not require extensive regression testing when the operating system is updated.
The kernel intercepts all requests for files, including those that reside in Sun QFS file systems. If a file is identified as a Sun QFS file, the kernel passes the request to the appropriate file system for handling. Sun QFS file systems are identified as type samfs in the /etc/vfstab file and through the mount command.
A Sun QFS shared file system is a distributed file system that can be mounted on multiple Oracle Solaris OS host systems. In a Sun QFS shared file system environment, one Oracle Solaris OS host acts as the metadata server for the file system, and additional hosts can be configured as clients. You can configure more than one host as a potential metadata server, but only one host can be the metadata server at any one time. There is no limit to the number of Sun QFS shared file system mount points.
The advantage of the Sun QFS shared file system is that file data passes directly from the Fibre Channel disks to the hosts. Data travels via local path I/O (also known as direct access I/O). This method is in contrast to the network file system (NFS), which transfers data over the network.
The shared file system can be implemented either as a Sun QFS shared file system or as a SAM-QFS shared file system. It can use either ms or ma file system types.
Sun QFS shared file systems do not support the following:
Certain file types:
b– Block special files
c– Character special files
p– FIFO (named pipe) special files
Segmented files. You cannot implement a SAM-QFS shared file system in a segmented-file environment.
Mandatory locks. An EACCES error is returned if the mandatory lock is set. Advisory locks are supported, however. For more information about advisory locks, see the fcntl(2) man page.
For more information about shared file systems, see Chapter 5, Configuring a Shared File System.