Using The CacheFS File System (Tasks)

This chapter describes how to set up and maintain CacheFS™ file systems.

This is a list of task maps in this chapter.

• "High-Level View of Using the CacheFS File System (Task Map)"

• "Creating and Mounting a CacheFS File System (Task Map)"

• "Maintaining a CacheFS File System (Task Map)"

• "Packing a Cached File System (Task Map)"

• "Collecting CacheFS Statistics (Task Map)"

For information on troubleshooting CacheFS errors, see "Troubleshooting cachefspack Errors".

High-Level View of Using the CacheFS File System (Task Map)

Use this task map to identify all the tasks for using CacheFS file systems. Each task in this map points to a series of additional tasks such as creating and mounting the CacheFS file systems, and packing and maintaining the cache.

Overview of the CacheFS File System

The CacheFS file system is a general purpose caching mechanism that improves NFS server performance and scalability by reducing server and network load. Designed as a layered file system, the CacheFS file system provides the ability to cache one file system on another. In an NFS environment, the CacheFS file system increases the client per server ratio, reduces server and network loads, and improves performance for clients on slow links, such as Point-to-Point Protocol (PPP).

How a CacheFS File System Works

You create a CacheFS file system on a client system so that file systems you cache can be accessed by the client locally instead of across the network. The following figure shows the relationship of the components that are involved in using CacheFS file system.

Figure 40-1 How a CacheFS File System Works

The back file system is the file system that you specify to be mounted in the cache, which can be either NFS or HSFS (High Sierra File System). When the user attempts to access files that are part of the back file system, those files are placed in the cache. The front file system is the file system that is mounted in the cache and is accessed from the local mount point. The front file system type must be UFS.

To the user, the initial request to access a file in a CacheFS file system might seem slow, but subsequent uses of the same file are faster.

CacheFS File System Structure and Behavior

Each cache has a set of parameters that determines how it behaves and its structure. The parameters are set to default values which are listed in the following table. The default values specify that the entire front file system is used for caching, which is the recommended method of caching file systems.

Table 40-1 CacheFS File System Parameters and Their Default Values

Typically, you should not change any of these parameter values. They are set to default values to achieve optimal cache behavior. However, you might want to modify the maxblocks and maxfiles values if you have some room in the front file system that is not used by the cache, and you wish to use it for some other file system. You do so by using the cfsadmin command. For example:

$ cfsadmin -o maxblocks=60

Creating and Mounting a CacheFS File System (Task Map)

Use the procedures in this table to create and mount a CacheFS file system.

How to Create the Cache

1. Become superuser on the client system.

2. Create the cache.

   # cfsadmin -c /cache-directory

   cache-directory indicates the name of the directory where the cache resides.

   For more information, see cfsadmin(1M).

   ---

   Note - After you have created the cache, do not perform any operations within the cache directory itself. Doing so could cause conflicts within the CacheFS software.

   ---

Example--Creating the Cache

The following example shows how to create a cache in the /local/mycache directory by using the default cache parameter values.

# mkdir /local
# cfsadmin -c /local/mycache

Mounting a File System in the Cache

You specify a file system to be mounted in the cache so that users can locally access files in that file system. The files do not actually get placed in the cache until the user accesses the files.

The following table describes three ways to mount a CacheFS file system.

Choose the method of mounting file systems that best suits your environment.

You can mount only file systems that are shared. For information on sharing file systems, see share(1M).

Note - The caching of the root (/) and /usr file systems is not supported in a CacheFS file system.

How to Mount a CacheFS File System (mount)

1. Become superuser on the client system.

2. Create the mount point, if necessary.

   # mkdir /mount-point

   You can create the mount point from anywhere but it must be a UFS file system. The CacheFS options used with the mount command, as shown in the next step, determine that the mount point you create is cached in the cache directory you specify.

3. Mount a file system in the cache.

   # mount -F cachefs -o backfstype=fstype,cachedir=/cache-directory[,options] /back-filesystem /mount-point

   fstype	Indicates the file system type of the back file system (can be either NFS or HSFS).
   /cache-directory	Indicates the name of the UFS directory where the cache resides. This name is the same name you specified when you created the cache in "How to Create the Cache".
   options	Specifies other mount options that you can include when you mount a file system in a cache. For a list of CacheFS mount options, see mount_cachefs(1M).
   /back-filesystem	Specifies the mount point of the back file system to cache. If the back file system is an NFS file system, you must specify the host name of the server from which you are mounting the file system and the name of the file system to cache (separated by a colon). For example, merlin: /data/abc.
   /mount-point	Indicates the directory where the file system is mounted.

4. Verify that the cache you created was actually mounted.

   # cachefsstat /mount-point

   The /mount-point is the CacheFS file system that you created.

   For example:

   # cachefsstat /docs /docs cache hit rate: 100% (0 hits, 0 misses) consistency checks: 1 (1 pass, 0 fail) modifies: 0 garbage collection: 0

   If the file system was not mounted in the cache, you see an error message similar to the following:

   # cachefsstat /mount-point cachefsstat: mount-point: not a cachefs mountpoint

   For more information about the cachefsstat command, see "Collecting CacheFS Statistics".