Shared File System Mount Options

You can specify most mount options by using the mount command, by entering them in the /etc/vfstab file, or by entering them in the samfs.cmd file. For example, the following /etc/vfstab file includes mount options for a shared file system:

sharefs1 - /sfs samfs - no shared,mh_write

You can change some mount options dynamically by using the samu(1M) operator utility. For more information about these options, see Chapter 13, Using the samu Operator Utility.

For more information about any of these mount options, see mount_samfs(1M) in Sun QFS and Sun Storage Archive Manager 5.3 Reference Manual or see the cross-references mentioned in their descriptions.

Mounting in the Background: (bg Option)

The bg mount option specifies that if the first mount operation fails, subsequent attempts at mounting should occur in the background. By default, bg is not in effect, and mount attempts continue in the foreground.

Reattempting a File System Mount: (retry Option)

The retry mount option specifies the number of times that the system should attempt to mount a file system. The default is 10000.

Declaring a Sun QFS Shared File System: (shared Option)

The shared mount option declares a file system to be a Sun QFS shared file system. This option must be specified in the /etc/vfstab file in order for the file system to be mounted as a Sun QFS shared file system. The presence of this option in a samfs.cmd file or on the mount command does not cause an error condition, but it does not mount the file system as a shared file system.

Tuning Allocation Sizes: (minallocsz and maxallocsz Options)

The minallocsz and maxallocsz options to the mount command specify an amount of space, in kilobytes. These options set the minimum block allocation size. If a file is growing, the metadata server allocates blocks when an append lease is granted. Use -o minallocsz= n to specify the initial size of this allocation. The metadata server can increase the size of the block allocation depending on the application's access patterns up to but not exceeding the -o maxallocsz= n setting.

You can specify these mount options on the mount command line, in the /etc/vfstab file, or in the samfs.cmd file.

Using Leases in a Sun QFS Shared File System: (rdlease, wrlease, and aplease Options)

A lease grants a shared host permission to perform an operation on a file for as long as the lease is valid. The metadata server issues leases to each shared host, including itself. The leases are renewed as necessary to permit continued file operations. The possible file operations are as follows:

• A read lease enables existing file data to be read.

• A write lease enables existing file data to be overwritten.

• An append lease enables a file's size to be extended and enables newly allocated blocks to be written.

A shared host can continue to update leases for as long as necessary. The lease is transparent to the end user. The following table shows the mount options that enable you to specify the duration of each lease type.

Table 12-1 Lease-Related mount(1M) Options

All three leases enable you to specify an n such that 15 ≤ n ≤ 600. The default time for each lease is 30 seconds. A file cannot be truncated if a lease is in effect. For more information about setting these leases, see mount_samfs(1M) in Sun QFS and Sun Storage Archive Manager 5.3 Reference Manual.

If you change the metadata server because the current metadata server is down, you must add the lease time to the changeover time because all leases must expire before an alternate metadata server can assume control.

Setting a short lease time causes more traffic between the client hosts and the metadata server because the lease must be renewed after it has expired.

Enabling Multiple Host Reads and Writes: (mh_write Option)

By default, in a Sun QFS shared file system, multiple hosts can read the same file at the same time. If no host is writing to that file, I/O can be paged on all hosts. Only one host can append or write to a file at any one time.

The mh_write option controls write access to the same file from multiple hosts. If mh_write is specified as a mount option on the metadata server host, the Sun QFS shared file system enables simultaneous reads and writes to the same file from multiple hosts. If mh_write is not specified on the metadata server host, only one host can write to a file at any one time.

By default, mh_write is disabled, and only one host has write access to a file at any one time. The length of that time period is determined by the duration of the wrlease mount option. If the Sun QFS shared file system is mounted on the metadata server with the mh_write option enabled, simultaneous reads and writes to the same file can occur from multiple hosts.

The following table describes how file access from multiple hosts is affected depending on whether the mh_write option is enabled on the metadata server.

Table 12-2 File Access Based on the mh_write Option

The mh_write option does not change locking behavior. File locks behave the same regardless of whether mh_write is in effect. The mh_write option's effect is as follows:

• When mh_write is in effect, all hosts can read from and write to the same file simultaneously.

• When mh_write is not in effect, only one host can write to a given file during a given time interval, and no hosts can read from the file during that time interval.

Sun QFS shared file system maintains consistency between hosts. The first time that a host executes a read or write system call, it gets a lease, which enables it to read or write the file for some period of time. The existence of that lease prevents other hosts without mh_write from accessing the file. In particular, the lease can last longer than the duration of the system call that caused its acquisition.

When mh_write is not in effect, the Sun QFS shared file system should provide near-POSIX behavior for data reads and writes. For metadata, however, access time changes might not be seen immediately on other hosts. Changes to a file are pushed to disk at the end of a write lease. When a read lease is acquired, the system invalidates any stale cache pages so that the newly written data can be seen.

When mh_write is in effect, behavior might be less consistent. When there are simultaneous readers and writers, the Sun QFS shared file system switches all hosts accessing the file into direct I/O mode. Therefore, page-aligned I/O should be visible immediately to other hosts. However, non-page-aligned I/O can result in stale data being visible, or even written to the file, because the normal lease mechanism preventing such occurrences has been disabled.

You should specify the mh_write option only when multiple hosts need to write to the same file simultaneously and when applications perform page-aligned I/O. In other cases, data inconsistency could occur because even using flock() (which works with mh_write) to coordinate between hosts does not guarantee consistency.

For more information about mh_write, see mount_samfs(1M) in Sun QFS and Sun Storage Archive Manager 5.3 Reference Manual.

Setting the Minimum Number of Concurrent Threads: (min_pool Option)

The min_pool mount option sets the minimum number of concurrent threads for the Sun QFS shared file system. The default setting is min_pool=64 on Oracle Solaris systems. This setting means that at least 64 active threads will be in the thread pool on Oracle Solaris. You can adjust the min_pool setting to any value between 8 and 2048, depending on the Sun QFS shared file system's activity.

The min_pool mount option must be set in the samfs.cmd file. It will be ignored if set in the /etc/vfstab file or at the command line.

Retaining Cached Attributes: (meta_timeo Option)

The meta_timeo mount option determines how long the system waits between checks on the metadata information. By default, the system refreshes metadata information every three seconds. For example, an ls command entered in a Sun QFS shared file system with several newly created files might not return information about all the files until three seconds have passed. The syntax for the option is meta_timeo= n specifies a value such that 0 ≤ n ≤ 60.

Specifying Striped Allocation: (stripe Option)

By default, data files in the Sun QFS shared file system are allocated using the round-robin file allocation method. To specify that file data be striped across disks, you can specify the stripe mount option on the metadata host and all potential metadata hosts. Note that by default, unshared file systems allocate file data using the striped method.

In a round-robin allocation, files are created in a round-robin fashion on each slice or striped group. The maximum performance for one file will be the speed of a slice or striped group. For more information about file allocation methods, see Sun QFS File Systems Design Basics.

Specifying the Frequency With Which Metadata Is Written: (sync_meta Option)

You can set the sync_meta option to sync_meta=1 or sync_meta=0.

The default setting is sync_meta=1, which means that a Sun QFS shared file system writes file metadata to disk every time the metadata changes. This setting slows data performance but ensures data consistency. This setting must be in effect if you want to change the metadata server.

If you set sync_meta=0, the Sun QFS shared file system writes the metadata to a buffer before writing it to disk. This delayed write delivers higher performance but decreases data consistency after an unscheduled machine interruption.

Enabling WORM Functionality: (worm_capable and def_retention Options)

If you are using the optional WORM package, the worm_capable mount option enables the file system to support WORM files. The def_retention mount option sets the default retention time using the format def_retention=MyNdOhPm.

In this format, M, N, O, and P are non-negative integers and y, d, h, and m stand for years, days, hours, and minutes, respectively. Any combination of these units can be used. For example, 1y5d4h3m indicates 1 year, 5 days, 4 hours, and 3 minutes; 30d8h indicates 30 days and 8 hours; and 300m indicates 300 minutes. This format is backward compatible with the formula in previous software versions, in which the retention period was specified in minutes.

See Chapter 9, Configuring WORM-FS File Systems for more information about the WORM functionality.