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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 |
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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 |
2. About the Master Configuration File
4. Configuring the File System
5. Configuring a Shared File System
6. Administering File System Quotas
7. Advanced File System Topics
Using Daemons, Processes, and Tracing
Determining Which Processes Are Being Traced
Using the setfa Command to Set File Attributes
Selecting File Attributes for Files and Directories
Selecting a File Allocation Method and Stripe Width
Selecting a Striped Group Device
9. Configuring WORM-FS File Systems
11. Using QFS File Systems with SANergy (SAN-QFS)
A multireader file system consists of a single writer host and multiple reader hosts. The writer and reader mount options that enable the multireader file system are compatible with Sun QFS file systems only. The mount options are described in this section and in the mount_samfs(1M) man page.
You can mount the multireader file system on the single writer host by specifying the-o writer option with the mount command. The host system with the writer mount option is the only host system that is allowed to write to the file system. The writer host system updates the file system. You must ensure that only one host in a multireader file system has the file system mounted with the writer mount option enabled. If-o writer is specified, directories are written through to disk at each change and files are written through to disk at close.
 | Caution - The multireader file system can become corrupted if more than one writer host has the file system mounted at one time. The site administrator's responsibility should ensure that this situation does not occur. |
You can mount a multireader file system on one or more reader hosts by specifying the-o reader option with the mount command. There is no limit to the number of host systems that can have the multireader file system mounted as a reader.
A major difference between the multireader file system and a Sun QFS shared file system is that the multireader host reads metadata from the disk, and the client hosts of a Sun QFS shared file system read metadata over the network. The Sun QFS shared file system supports multireader hosts. In this configuration, multiple shared hosts can be adding content while multiple reader hosts are distributing content.
Note - You cannot specify the writer option on any host if you are mounting the file system as a Sun QFS shared file system. You can, however, specify the reader option. If you want a Sun QFS shared file system client host to be a read-only host, mount the Sun QFS shared file system on that host with the reader mount option. In addition, set the sync_meta mount option to 1 if you use the reader option in a Sun QFS shared file system. For more information about the Sun QFS shared file system, see Chapter 5, Configuring a Shared File System. For more information about mount options, see mount_samfs(1M) in Sun QFS and Sun Storage Archive Manager 5.3 Reference Manual.
You must ensure that all readers in a multireader file system have access to the device definitions that describe the ma device. Copy the lines from the mcf file that resides on the primary metadata server host to the mcf files on the alternate metadata servers. After copying the lines, you might need to update the information about the disk controllers because, depending on your configuration, disk partitions might not show up the same way across all hosts.
In a multireader file system environment, the Sun QFS software ensures that all servers accessing the same file system can always access the current environment. When the writer closes a file, the Sun QFS file system immediately writes all information for that file to disk. A reader host can access a file after the file is closed by the writer. You can specify the refresh_at_eof mount option to help ensure that no host system in a multireader file system gets out of sync with the file system.
By default, the metadata information for a file on a reader host is invalidated and refreshed every time a file is accessed. If the data changes, it is invalidated. This policy includes any type of access, whether through cat, ls, touch, open, or other methods. This immediate refresh rate ensures that the data is correct at the time the refresh is done, but it can affect performance. Depending on your site preferences, you can use the mount command's-o invalid=n option to specify a refresh rate between 0 seconds and 60 seconds. If the refresh rate is set to a small value, the Sun QFS file system reads the directory and other metadata information n seconds after the last refresh. More frequent refreshes result in more overhead for the system, but stale information can exist if n is nonzero.
| Caution - If a file is open for a read on a reader host, that file could be removed or truncated by the writer. Use another mechanism, such as application locking, to protect the reader from inadvertent writer actions. |
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