C H A P T E R 1

Overview

The Sun StorEdge QFS and Sun StorEdge SAM-FS file systems are configurable file systems that present a standard UNIX file system interface to users. TABLE 1-1 shows how these file systems can be used or combined with the storage and archive management (SAM) software.

TABLE 1-1 Product Overview
Product | Components
--- | ---
Sun StorEdge QFS file system | Sun StorEdge QFS standalone file system
Sun StorEdge SAM-FS file system | Standard file system plus the storage and archive management utility, SAM
Sun SAM-QFS file system | The Sun StorEdge QFS file system combined with the storage and archive management utilities found in the Sun StorEdge SAM-FS software.

Technologically, the two file systems are similar, but there are also differences between them. This chapter presents an overview of the features common to these file systems, highlights the features that differentiate the file systems, and explains the commands available with each file system. Specifically, this chapter is divided into the following sections:

- Common Features

- File System Differences

##

Common Features

The Sun StorEdge QFS and Sun StorEdge SAM-FS file systems do not require changes to user programs, nor are changes required to the UNIX kernel. These file systems share the features described in the following sections.

### `vnode` Interface

``The Sun StorEdge QFS and Sun StorEdge SAM-FS file systems are implemented using the standard Solaris operating system (OS) virtual file system (`vfs/vnode`) interface.

``By using the `vfs/vnode` interface, these file systems work with the standard Solaris OS kernel and require 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 StorEdge QFS and Sun StorEdge SAM-FS file systems. If the file is identified as a Sun StorEdge QFS or Sun StorEdge SAM-FS file, the kernel passes the request to the appropriate file system for handling. Sun StorEdge QFS and Sun StorEdge SAM-FS file systems are identified as type `samfs` in the `/etc/vfstab` file and on the `mount`(1M) command.

### Enhanced Volume Management

Sun StorEdge QFS and Sun StorEdge SAM-FS 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 let the file system know the relationships between the devices it controls. This is in contrast to most UNIX file systems that can address only one device or one portion of a device. Sun StorEdge QFS and Sun StorEdge SAM-FS file systems do not require any additional volume management applications. If you want to use mirroring for any devices in a Sun StorEdge QFS or Sun StorEdge SAM-FS environment, obtain an additional package, such as a logical volume manager.

The Sun StorEdge QFS and Sun StorEdge SAM-FS integrated volume management features use the standard Solaris OS device driver interface to pass I/O requests to and from the underlying devices. The Sun StorEdge QFS and Sun StorEdge SAM-FS software groups storage devices into family sets upon which each file system resides.

### Support for Paged and Direct I/O

Sun StorEdge QFS and Sun StorEdge SAM-FS file systems support two different types of I/O: paged (also called cached or buffered I/O) and direct. These I/O types are as follows:

- When paged I/O is used, user data is cached in virtual memory pages and the kernel writes the data to disk. The standard Solaris OS interfaces manage paged I/O. This is the default type of 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 Solaris OS `directio`(3C) function call or the `setfa`(1) command with its `-D` option. Large block, sequential, aligned I/O can realize substantial performance improvements by using direct I/O.

### Preallocation of File Space

You can use the `setfa`(1) command to preallocate contiguous disk space for fast sequential reads and writes.

### Application Programming Interface Routines

The application programming interface (API) routines enable a program to perform various specialized functions, such preallocating contiguous disk space or accessing a specific striped group. For more information about these routines, see the `intro_libsam`(3) man page.

### High Capacity

The Sun StorEdge QFS and Sun StorEdge SAM-FS file systems support files of up to 263 bytes in length. Such very large files can be striped across many disks or RAID devices, even within a single file system. This is true because Sun StorEdge QFS and Sun StorEdge SAM-FS file systems use true 64-bit addressing. This is in contrast to a standard UNIX file system (UFS), which is not a true 64-bit file system.

The number of file systems you can configure is virtually unlimited. The volume manager enables each file system to include up to 252 device partitions (typically disk). Each partition can include up to 4 terabytes of data. This configuration offers virtually unlimited storage capacity.

There is no predefined limit on the number of files on a Sun StorEdge SAM-FS 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 512 bytes of storage per file.

For a Sun StorEdge QFS file system, the inodes are located on the metadata device(s) and are separated from the file data devices. In practice, the size of your metadata (`mm`) devices sets the limit on the number of files in a Sun StorEdge QFS file system. You can increase maximum the number of files by adding more metadata devices. The hard limit on the number of files is 232-1 files, and the recommended limit is 107 files.

### Fast File System Recovery

A key function of a file system is the ability to recover quickly after an unscheduled outage. Standard UNIX file systems require a lengthy file system check (`fsck`(1M)) to repair inconsistencies after a system failure.

Sun StorEdge QFS and Sun StorEdge SAM-FS file systems often do not require file system checks after a disruption that prevents the file system from being written to to disk (using `sync`(1M)). In addition, they recover from system failures without using journaling. They accomplish this dynamically by using identification records, serial writes, and error checking for all critical I/O operations. After a system failure, Sun StorEdge QFS and Sun StorEdge SAM-FS file systems can be remounted immediately, even for multiterabyte-sized file systems.

### Adjustable Disk Allocation Unit

The disk allocation unit (DAU) is the basic unit of online storage. The Sun StorEdge QFS file systems include an adjustable DAU, which is useful for tuning the file system with the physical disk storage device and for eliminating the system overhead caused by read-modify-write operations. You can adjust the DAU size in multiples of 4 kilobytes.

##

File System Differences

The Sun StorEdge QFS and Sun StorEdge SAM-FS file systems share many features, and these are described in Common Features. This section, however, describes the areas in which they differ. One area of difference is performance. The Sun StorEdge QFS file system provides the ability to attain raw, device-rated disk speeds with the administrative convenience of a file system. The following sections note other ways in which the file systems differ.

### Metadata Storage

File systems use metadata to reference file and directory information. Typically, metadata resides on the same device as the file data. This is true for the Sun StorEdge SAM-FS file system.

The Sun StorEdge QFS file system separates the file system metadata from the file data by storing them on separate devices. The Sun StorEdge 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.

Both the Sun StorEdge QFS and Sun StorEdge SAM-FS file systems store inode metadata information in a separate file. This enables the number of files, and the file system as a whole, to be enlarged dynamically.

### Support for Multiple Striped Groups

To support multiple RAID devices in a single file system, striped groups can be defined in Sun StorEdge QFS file systems. You can optimize disk block allocation for a striped group. This reduces the overhead for updating the on-disk allocation map. Users can assign a file to a striped group either through an API routine or by using the `setfa`(1) command.

### SAM Interoperability

The Sun StorEdge SAM-FS file system combines file system features with the storage and archive management utility, SAM. Users can read and write files directly from magnetic disk, or they can access archive copies of files as though they were all on primary disk storage.

The Sun StorEdge QFS file system can be used as a standalone file system, or it can be used in conjunction with the storage and archive manager, SAM. If you are licensed for both Sun StorEdge QFS and Sun StorEdge SAM-FS, it is called Sun SAM-QFS.

When possible, Sun StorEdge SAM-FS sofware uses the standard Solaris OS disk and tape device drivers. For devices not directly supported under the Solaris OS, such as certain automated library and optical disk devices, Sun Microsystems provides special device drivers in the Sun StorEdge SAM-FS software package.

### Sun Cluster Interoperability

The Sun StorEdge QFS file system is supported as a local file system and as a highly available file system in a Sun Cluster environment. The Sun StorEdge SAM-FS file system is not supported in a Sun Cluster environment.

### Sun StorEdge QFS Shared File System Support

The shared file system can be implemented as either a Sun StorEdge QFS shared file system or as a Sun SAM-QFS shared file system. A shared file system enables you to implement a distributed file system that can be mounted on multiple Sun Solaris host systems.

Sun StorEdge QFS shared file systems do not support the following file types:

- `b` -- block special files

- `c` -- character special files

- `p` -- FIFO (named pipe) special files

The shared file system does not support segmented files. You cannot implement a Sun SAM-QFS shared file system in a Sun Cluster environment.

For more information about this file system, see the Sun StorEdge QFS Shared File System.

Copyright © 2004, Sun Microsystems, Inc. All rights reserved.