What are Sun StorageTek QFS and SAM

Sun StorageTek QFS is a shared file system. QFS is the only shared file system Sun offers which can be shared or combined with Sun StorageTek SAM to provide a complete data management solution for managing data throughout its lifecycle across tiers of storage.

Why consider Sun StorageTek QFS?

If you want to consolidate your business data and provide shared access in multi-platform environments you will need the QFS shared file system software. This file system allows users to easily share and cost effectively manage growing volumes of business data. Data services in the QFS shared environment can be expanded to include the Tiered Storage capabilities of the Sun StorageTek SAM storage archive management software.

About Sun StorageTek QFS

The Sun StorageTek QFS file system is a configurable file system that presents a standard UNIX file system (UFS) interface to users. TABLE 1-1 shows how the file system can be used or combined with the storage and archive management (Sun StorageTek SAM) software.

 TABLE 1-1 Product Overview |=
Product

The Sun StorageTek QFS file system does not require changes to user programs or to the UNIX kernel. Some of the features of the Sun StorageTek QFS file system are described in the following sections.

Volume Management

Sun StorageTek 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 is in contrast to most UNIX file systems, which can address only one device or one portion of a device. Sun StorageTek QFS file systems do not require additional volume management applications. However, if you want to use mirroring for devices in a Sun StorageTek QFS environment, you must obtain an additional package, such as a logical volume manager.

The Sun StorageTek QFS 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 StorageTek QFS software groups storage devices into family sets upon which each file system resides.

Support for Paged and Direct I/O

The Sun StorageTek QFS file system supports two different types of I/O: paged (also called cached or buffered I/O) and direct. These I/O types perform 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 for Sun StorageTek QFS.
• 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. By using direct I/O, you can realize substantial performance improvements for large block, sequential, aligned I/O.

High Capacity

The Sun StorageTek QFS software supports 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 StorageTek QFS file systems use true 64-bit addressing, in contrast to standard UNIX file systems, which 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. 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 StorageTek 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 512 bytes of storage per file.

In a Sun StorageTek QFS file system, the inodes are located on the metadata devices and are separated from the file data devices. In practice, the size of your metadata (mm) devices limits the number of files in a Sun StorageTek 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 232-1 files, and the recommended limit is 107 files.

Fast File System Recovery

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(1M)) to repair inconsistencies after a system failure.

A Sun StorageTek 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 sync(1M)). In addition, Sun StorageTek QFS file systems 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, even multiterabyte-sized Sun StorageTek QFS file systems can be remounted immediately.

Metadata Storage

File systems use metadata to reference file and directory information. Typically, metadata resides on the same device as the file data. However, the Sun StorageTek QFS file system has the option of separating the file system metadata from the file data by storing them on separate devices. The Sun StorageTek 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 StorageTek QFS 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.

vnode Interface

The Sun StorageTek QFS file system is implemented through the standard Solaris OS virtual file system (vfs/vnode) interface.

By using the vfs/vnode interface, the file system works with the standard 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 StorageTek QFS file systems. If a file is identified as a Sun StorageTek QFS file, the kernel passes the request to the appropriate file system for handling. Sun StorageTek QFS file systems are identified as type samfs in the /etc/vfstab file and through the mount(1M) command.

Shared File System Support

A Sun StorageTek QFS shared file system is a distributed file system that can be mounted on multiple Solaris OS host systems. In a Sun StorageTek QFS shared file system environment, one 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 StorageTek QFS shared file system mount points.

The advantage of the Sun StorageTek 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 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 StorageTek QFS shared file system or as a SAM-QFS shared file system. It can use either ms or ma file system types.

Sun StorageTek QFS shared file systems do not support the following:

• These 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) system call.

Linux Client Support

Within a shared file system, the Sun StorageTek QFS software can be installed on Linux as well as Solaris clients. The Sun StorageTek QFS Linux Client software supports the following Linux distributions:

• Red Hat Enterprise Linux 3.0 (UD-5 and UD8) for x86/x64 platforms (Sun StorageTek QFS shared client only)
• Red Hat Enterprise Linux 4.0 (UD-2 and UD-4) for x64 platforms (Sun StorageTek QFS shared client only)
• SuSE Linux Enterprise Server 8 (service pack 4) for x64 platforms (Sun StorageTek QFS shared client only)
• SuSE Linux Enterprise Server 9 (service pack 2) for x64 platforms and SGI Altix Itanium systems (Sun StorageTek QFS shared client only)
• SuSE Linux Enterprise Server 10 for x64 platforms (Sun StorageTek QFS shared client only)

Unlike shared Sun StorageTek QFS Solaris clients, the Linux client is restricted to client-only behavior. It cannot be configured as a potential metadata server. The Linux client supports interaction with Sun StorageTek SAM software, but does not support Sun StorageTek SAM commands such as stage, archive, release, and samu. It has Sun StorageTek QFS file system functionality only.

For more information about the Sun StorageTek QFS Linux client software, see the Sun StorageTek QFS Linux Client Guide.

Additional File System Features

The following additional features are also supported by the Sun StorageTek QFS file system:

• 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 (API) routines - API routines enable a program to perform various specialized functions, such as preallocating contiguous disk space or accessing a specific striped group. For more information about these routines, see the intro_libsam(3) man page.
• Adjustable disk allocation units (DAUs) -The DAU is the basic unit of online storage. The Sun StorageTek QFS file system software includes an adjustable DAU, which is useful for tuning file systems 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.
• Support for multiple striped groups - To support multiple RAID devices in a single file system, Sun StorageTek QFS software supports the definition of striped groups. You can optimize disk block allocation for a striped group, thereby reducing 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.
• Sun Cluster system interoperability - The Sun StorageTek QFS file system is supported as a local file system and as a highly available file system in a Sun Cluster environment.

Archive Products

About Sun StorageTek SAM

The Sun StorageTek SAM environment provides a configurable file system with storage, archive management, and retrieval capabilities. The Sun StorageTek SAM software archives files by copying the files from online disk cache to archive media. The archive media can consist of disk slices in another file system or it can consist of removable tape or magneto-optical cartridges in automated or manually loaded storage devices. The Sun StorageTek SAM software automatically maintains online disk space at site-specified usage thresholds. It releases disk space associated with archived file data and restores the files to online disk when they are needed.

Capabilities

The Sun StorageTek SAM storage and archive management software includes a high-performance UNIX file system that resides in the server's disk cache. For more information about the file system itself, see the Sun StorageTek Storage Archive Manager File System Configuration and Administration Guide.The other components that reside in the Sun StorageTek SAM environment are as follows:

The archiver automatically copies online disk cache files to archive media. The archive media can consist of either online disk files or removable media cartridges. By default, the archiver automatically creates one archive copy of all files in a Sun StorageTek SAM file system and writes the archive copy to archive media. You can configure the archiver to create up to four archive copies on a variety of archive media. If a file is segmented, each segment is treated as a file and is archived separately. The archiving process is initiated after disk-based files match a site-definable set of selection criteria.

The releaser automatically maintains the file system's online disk cache at site-specified percentage usage thresholds by freeing disk blocks occupied by eligible archived files.

Releasing is the process of freeing primary (disk) storage that is used by an archived file's data. Two threshold values, the high-water mark and the low-water mark, both expressed as a percentage of total disk space, are used to manage online disk cache free space. When online disk consumption exceeds the high-water mark, the system automatically begins releasing the disk space occupied by eligible archived files. Disk space occupied by archived file data is released until the low-water mark is reached. Files are selected for release depending on their size and age. The first portion of a file can be retained on disk for speedy access and for masking staging delays. If a file has been archived in segments, portions of the file can be released individually.

The stager restores file data to the disk cache. When a user or process requests file data that has been released from disk cache, the stager automatically copies the file data back to the online disk cache.

When a file whose data blocks have been released is accessed, the stager automatically stages the file or file segment data back to online disk cache. The read operation tracks along directly behind the staging operation, allowing the file to be immediately available to an application before the entire file is completely staged.
 The Sun StorageTek SAM software processes stage request errors automatically. If a stage error is returned, the system attempts to find the next available archive copy of the file. Stage errors that can be automatically processed include media errors, unavailability of media, unavailability of an automated library, and other.

The recycler clears archive volumes of expired archive copies and makes volumes available for reuse.

As users modify files, archive copies associated with the old versions of these files are considered to be expired on their archive media. Such copies are no longer needed, so they can be purged from the system. The recycler identifies the archive volumes with the largest proportions of expired archive copies and preserves the unexpired copies by moving them to separate volumes.
 If a removable media volume contains only expired copies, you can take one of the following actions:

• Relabel the volume for immediate reuse.
• Export the volume to offsite storage as a historical record of file changes. You can use standard UNIX utilities to restore previous versions of files from expired archive copies.

The recycling process is transparent to end users.