IBM Certification Study Guide AIX V4.3 System Support

5.5 Managing Journaled File Systems

A file system is a set of files, directories, and other structures. File systems maintain information and identify of the location of a file or directory's data. In addition to files and directories, file systems contain a boot block, a superblock, bitmaps, and one or more allocation groups. An allocation group contains disk i-nodes and fragments.

The following three types of file systems are supported on an AIX system.

Journaled File System: This native file system type is called the journaled file system (JFS). Each journaled file system resides on a separate logical volume. The operating system mounts journaled file systems during initialization.
Network File System: The network file system (NFS) is a distributed file system that allows users to access files and directories located on remote computers and use those files and directories as if they are local.
CD-ROM File System: The CD-ROM file system (CDRFS) is a file system type that allows you to access the contents of a CD-ROM through the normal file system interfaces.

The Journaled File System (JFS) divides the logical volume into a number of fixed size units called logical blocks. The logical blocks in the file system are organized as follows:

Logical Block 0: The first logical block in the file system is reserved and available for a bootstrap program or any other required information; this block is unused by the file system.
Superblock: The first and thirty-first logical blocks are reserved for the superblock (logical block 31 being a backup copy). The super block contains information such as the overall size of the file system in 512 byte blocks, the file system name, file system log device address (logs will be covered later in this section), version number, and file system state.
Allocation Groups: The rest of the logical blocks in the file system are divided into a number of allocation groups. An allocation group consists of data blocks and i-nodes to reference those data blocks when they are allocated to directories or files.

5.5.1 Characteristics of Journaled File System

The size for a journaled file system (JFS) is defined when the file system is created considering the following parameters:

Number of i-nodes
Allocation group size
File system fragment addressability
Journaled file system log size
Maximum journaled file system size

5.5.1.1 Number of I-nodes

The total number of i-nodes in a file system limits the total number of files and the total size of the file system. The JFS provides the nbpi (number of bytes per i-node) parameter that affects the number of i-nodes in a file system. JFS supports nbpi values of 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, and 131072. The values 32768, 65536, and 131072 only apply to AIX Version 4.2 or later.

For example, to create an 8 MB file system with an nbpi value of 4096, an i-node will be generated for each 4096 bytes of data. This would result in a maximum of 2048 i-nodes for an 8 MB file system, which means that if every file in the file system is ideally 4 KB in length, a maximum of 2048 files can be created in the file system.

The JFS restricts all file systems to 16 MB (224) i-nodes.

5.5.1.2 Allocation Group Size

AIX Version 4.2 or later supports various allocation group sizes. The JFS segregates file system space into groupings of i-nodes and disk blocks for user data. These groupings are called allocation groups. The allocation group size can be specified when the file system is created. The allocation group sizes are 8 MB, 16 MB, 32 MB, and 64 MB. Each allocation group size has an associated nbpi range. The ranges are defined by the following table:

Table 10: Allowable nbpi Values

5.5.1.3 File System Fragment Addressability

The JFS supports four fragment sizes: 512, 1024, 2048, and 4096 byte units of contiguous disk space. The JFS maintains fragment addresses in i-nodes and indirect blocks as 28-bit numbers. Each fragment must be addressable by a number from 0 to (228).

5.5.1.4 Journaled File System Log Size

Multiple journaled file systems use a common log, called a JFS log, configured to be 4 MB in size. For example, after initial installation, all file systems within the root volume group use logical volume hd8 as a common JFS log. The default logical volume partition size is 4 MB, and the default log size is one partition, therefore, the root volume group normally contains a 4 MB JFS log. When file systems exceed 2 GB or when the total amount of file system space using a single log exceeds 2 GB, the default log size needs to be increased. The JFS log is limited to a maximum size of 256 MB.

5.5.1.5 Maximum Journaled File System Size

The maximum JFS size is defined when the file system is created. For example, selecting an nbpi ratio of 512 will limit the file system to a size of 8 GB (512 * 228 = 8 GB). When creating a JFS file system, the factors listed (nbpi, fragment size, and allocation group size) need to be weighed carefully. The file system size limitation is the minimum of NPBI * 224 or Fragment Size * 228.

5.5.2 Creating a File System

Every file system in AIX corresponds to a logical volume. In order to create a journaled file system use the following SMIT hierarchy.

Executing the SMIT fast path command smitty crjfs will show a screen similar to Figure 75.

Figure 75: smitty crjfs - Step 1
Select Add a Standard Journaled File System to add a new journaled file system. A screen similar to Figure 76 is displayed.

Figure 76: crjfs - Step 2
Select the volume group you want to add this new file system to by using the arrow keys. In this case, since there is only one volume group (rootvg), only rootvg is displayed. Select rootvg as your target volume group by pressing the Enter key.
Once you select the target volume group, a screen similar to Figure 77 is displayed.

Figure 77: crjfs - Step 3

In the Size of file system (in 512 byte blocks) parameter, enter the size of the file system you want to create. For example if you want to create a file system of 4 MB size, you can simply multiply the number of megabytes (4 in this case) with 2048 to get 512-byte blocks you will need to create a file system this large (8192 in this case).

Note

In AIX, all of the I/O is in 4 KB blocks, however, space is allocated in multiples of 512 byte blocks. This is done just to remain consistent with other UNIX systems. The smallest file system that you can create is equal to one PP, therefore, even if you mention the number of blocks to be less than one PP, the system will still create a file system equal to one PP. The following example shows how to calculate the number of blocks for a given amount of space in MB.

Since
512 bytes = 1 block
Therefore
1024 bytes = 2 blocks
and
1 MB = 2*1024 blocks
Therefore
x MB = x * 2048 blocks (Answer)

This indicates that the equivalent number of blocks for a file system of 2 MB are 4096 (Enter this number in the Size of File System field).

Next, in the MOUNT POINT parameter enter the full path where you want your file system to attach itself to the file system hierarchy. A mount point is a directory or file at which the new file system, directory, or file is made accessible.
Press Enter to create the journaled file system. The screen shown in Figure 78 indicates the successful completion of the process.

Figure 78: crjfs- Step 4

Note
In AIX, all of the I/O is in 4 KB blocks, however, space is allocated in multiples of 512 byte blocks. This is done just to remain consistent with other UNIX systems. The smallest file system that you can create is equal to one PP, therefore, even if you mention the number of blocks to be less than one PP, the system will still create a file system equal to one PP. The following example shows how to calculate the number of blocks for a given amount of space in MB. Since 512 bytes = 1 block Therefore 1024 bytes = 2 blocks and 1 MB = 21024 blocks Therefore x MB = x 2048 blocks (Answer) This indicates that the equivalent number of blocks for a file system of 2 MB are 4096 (Enter this number in the Size of File System field).

Alternatively, you can achieve the same task on the command line using the following command:

crfs -v jfs -g rootvg -a size=8192 -m /dummy

This will create a journaled file system of 8 MB with /dummy as the mount point in the rootvg volume group.

5.5.3 Mounting a File System

Mounting is a concept that makes file systems, files, directories, devices, and special files available for use at a particular location. It is the only way a file system is made accessible. Once you have created the file system, the next task is to make it available to your users. In order to do that, you must know how AIX manages the patching of the newly created file systems into its file tree using the mount points.

Figure 79 shows a file system mount point (/u/dick) before a file system is mounted over it.

Figure 79: File Tree View before Mounting

Figure 80 shows a mounted file system /u/dick over the /u/dick mount point.

Figure 80: File Tree View after Mounting

Note

When a file system is mounted over a directory, the permissions of the root directory of the mounted file system take precedence over the permissions of the mount point.
A common problem is failure of the pwd command. Without search permission in the mounted-over directory, the pwd command returns the following message.
pwd: Permission denied
This problem can be avoided by always setting the permissions of the mounted-over directory to at least 111.

Note
When a file system is mounted over a directory, the permissions of the root directory of the mounted file system take precedence over the permissions of the mount point. A common problem is failure of the `pwd` command. Without search permission in the mounted-over directory, the `pwd` command returns the following message. `pwd: Permission denied` This problem can be avoided by always setting the permissions of the mounted-over directory to at least 111.

5.5.3.1 Mounting a File System through Command Line

The following command shows how to mount a file system (/FileSystemX).

mount /FileSystemX

Alternatively, if you know the name of the device associated with your file system you can use the device name to mount your newly created file system.

If you want to mount all the file systems, you can use the following command to mount all the file systems at one time.

mount {-a|all}

5.5.3.2 Mounting a File System through SMIT

A file system can be also be mounted using the following SMIT fast path hierarchy.

Executing smitty mount will display the screen shown in Figure 81.

Figure 81: Mount File System - Step 1
Use the arrow keys to move the cursor down and select Mount a File System by pressing the Enter key. A screen similar to Figure 82 is shown:

Figure 82: Mount File System - Step 2
Use the arrow keys to move down to DIRECTORY over which to mount.
Press F4 to get a list of the mount points that you have defined for your file system. (Refer to 5.5.2 Creating a File System, to see how you created a file system, and notice that you created a mount point for your file system. You will use the same mount point to make your file system available to the users). Pressing F4 shows a screen similar to Figure 83.

Figure 83: Mount FIle System - Step 3
Use the arrow keys to select the file system you want to mount. Press Enter to make the selection. This will display the mount point you just selected in the DIRECTORY over which to mount field.
Press Enter again and wait for the SMIT ok prompt, which indicates the successful completion of the process.

5.5.3.3 Automatic Mounting

Mounts can be set to occur automatically during system initialization. There are two types of automatic mounts:

Those mounts that are required to boot and run the system. These file systems are explicitly mounted by the boot process. The stanzas of such file systems in the /etc/filesystems file have mount =automatic. When the multi-user initialization starts, the /etc/rc script does not try to mount these file systems again when it executes the mount all command. Similarly, when the umount all command is executed, these file systems are not unmounted.
The second type of automatic mount is user-controlled. These file systems are mounted by the /etc/rc script when it issues the mount all command. The stanzas of user-controlled automatic mounts have mount = true in /etc/filesystems.

You can specify a file system to be mounted automatically when you either use the mount all command or the by the /etc/rc script at the initialization time. You can achieve this by setting the Mount AUTOMATICALLY at system restart parameter to TRUE when you are creating a file system. (See Figure 77)

5.5.3.4 Displaying Mounted File Systems

The following example shows the use of command mount without a flag to display information about all the currently mounted file systems.


# mount
node       mounted        mounted over    vfs       date        options
-------- ---------------  ---------------  ------ ------------ ---------------
         /dev/hd4         /                jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd2         /usr             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd9var      /var             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd3         /tmp             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/lv01        /var/dce         jfs    Oct 25 18:21 rw,log=/dev/hd8
         /dev/hd1         /home            jfs    Oct 27 15:14 rw,log=/dev/hd8
         /dev/lvtest      /test            jfs    Oct 27 15:17 rw,log=/dev/hd8
         /dev/lv07        /auto1           jfs    Oct 27 15:34 rw,log=/dev/hd8

5.5.4 Removing a File System

The following example shows the steps involved to remove a file system.

Using the mount command to check the file systems that are currently mounted will display the following screen.


# mount 
node       mounted        mounted over    vfs       date        options
-------- ---------------  ---------------  ------ ------------ ---------------
         /dev/hd4         /                jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd2         /usr             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd9var      /var             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/hd3         /tmp             jfs    Oct 25 18:20 rw,log=/dev/hd8
         /dev/lv01        /var/dce         jfs    Oct 25 18:21 rw,log=/dev/hd8
         /dev/hd1         /home            jfs    Oct 27 15:14 rw,log=/dev/hd8
         /dev/lvtest      /test            jfs    Oct 27 15:17 rw,log=/dev/hd8
         /dev/lv07        /auto1           jfs    Oct 27 15:34 rw,log=/dev/hd8

Identify if the file system you want to remove is shown in the list.

Yes
Continue with Step 3.
No
Go to Step 5.
Unmount the file system by using the umount command.
```
umount <filesystem name>
```
Repeat Step 1 to check whether the file system has successfully been unmounted.

Alternatively, using the SMIT fast path command smitty rmjfs to remove a journaled file system will display a screen similar to the one shown in Figure 84.

Figure 84: rmjfs - Step 1

Press F4 to get a list of all the file systems that are defined on the system. You will obtain a screen similar to Figure 85.

Figure 85: rmjfs - Step 2
Select the file system to be removed using the arrow keys and press Enter.
The name of the file system you just selected will be shown in the FILE SYSTEM name parameter.
If you want to keep the directory name that was used to mount this file system, press Enter to complete the command, otherwise change the Remove Mount Point parameter to YES and press Enter to complete the process.

5.5.5 Increasing the Size of a File System

AIX provides you the facility to increase the size of a file system dynamically, provided you have enough free space available on your disk. File systems that are low on space might create unanticipated problems.

Note

Whenever a file system is full, the system cannot write to it and returns you the following error.
There is not enough room in the file system

Note
Whenever a file system is full, the system cannot write to it and returns you the following error. There is not enough room in the file system

5.5.5.1 Increasing File System Size Using the Command Line

A file system can be increased by using the chfs command as shown in the following steps.

Use the df command to find out the current size of the file system.
Calculate the number of blocks you need to add.

On the command line, enter the following command:

chfs -a size=<new size in 512-byte blocks> <file system name>
Filesystem size changed to <new size in 512-byte blocks>

5.5.5.2 Increasing the Size of a File System Using SMIT

To increase the file system size using the SMIT fast path command (smitty chjfs), do the following steps.

Executing the smitty chjfs will display a screen similar to Figure 86.

Figure 86: chjfs - Step 1
Use the arrow keys to select the file system you want to change, and press the Enter key. A screen similar to Figure 87 will be shown, which will report the current file system attributes.

Figure 87: chjfs - Step 2
Enter the new file system size that you calculated in the SIZE of file system (in 512 byte block) field.
Press Enter. The SMIT OK prompt will indicate the successful completion of the process.

5.5.6 Checking the File System Consistency

The fsck command checks file system consistency and interactively repairs the file system. The general syntax of the fsck command is as follows:

fsck [ -n ] [ -p ] [ -y ] [ -dBlockNumber ] [ -f ] [ -ii-NodeNumber ] [ -o Options ] [ -tFile ] [ -V VfsName ] [ FileSystem1 - FileSystem2 ... ]

The flags commonly used with the fsck command and their meanings are shown in the following table.

Table 11: fsck Command Flags

The fsck command checks and interactively repairs inconsistent file systems. You should run this command before mounting any file system. You must be able to read the device file on which the file system resides (for example, the /dev/hd0 device).

Normally, the file system is consistent and the fsck command merely reports on the number of files, used blocks, and free blocks in the file system. If the file system is inconsistent, the fsck command displays information about the inconsistencies found and prompts you for permission to repair them. If the file system cannot be repaired, restore it from backup.

Mounting an inconsistent file system may result in a system crash. If you do not specify a file system with the FileSystem parameter, the fsck command will check all the file systems with attribute check=TRUE in /etc/filesystems.

Note

By default, the /, /usr, /var, and /tmp file systems have the check attribute set to False (check=false) in their /etc/filesystem stanzas. The attribute is set to False for the following reasons:

The boot process explicitly runs the fsck command on the /, /usr, /var, and /tmp file systems.
The /, /usr, /var, and /tmp file systems are mounted when the /etc/rc file is executed. The fsck command will not modify a mounted file system and fsck results on mounted file systems are unpredictable

Note
By default, the /, /usr, /var, and /tmp file systems have the check attribute set to False (check=false) in their /etc/filesystem stanzas. The attribute is set to False for the following reasons: The boot process explicitly runs the `fsck` command on the /, /usr, /var, and /tmp file systems. The /, /usr, /var, and /tmp file systems are mounted when the /etc/rc file is executed. The `fsck` command will not modify a mounted file system and `fsck` results on mounted file systems are unpredictable

5.5.7 Initializing the JFS Log Device

The logform command initializes a logical volume for use as a JFS log device, which stores transactional information about file system metadata changes and can be used to roll back incomplete operations if the machine crashes. Following is the general syntax of the logform command.

logform LogName

Note

The logform command is destructive; it wipes out all data in the logical volume.
Accidentally running this on a file system completely destroys the file system's data. The logform command should only be run on CLOSED logical volumes. If a log device is open due to its use by a mounted file system, the file system should be unmounted prior to running logform against the log device.The logform command destroys all log records on existing log devices, which may result in file system data loss. You can check to ensure that the log device is closed by running the following:
lsvg -l VGname

Note
The `logform` command is destructive; it wipes out all data in the logical volume. Accidentally running this on a file system completely destroys the file system's data. The `logform` command should only be run on CLOSED logical volumes. If a log device is open due to its use by a mounted file system, the file system should be unmounted prior to running `logform` against the log device.The `logform` command destroys all log records on existing log devices, which may result in file system data loss. You can check to ensure that the log device is closed by running the following: lsvg -l VGname

5.5.8 How to Add Additional JFS Logs

A file system log is a formatted list of file system transaction records. The log for this system is called the journaled file system (JFS) log and is used when the system goes down before the transactions have been completed. The JFS log ensures file system integrity, but not necessarily data integrity. A dedicated disk is created on hd8 for rootvg when the system is installed. The JFS log size is 4 MB. You can also create a JFS log on a separate disk for other volume groups, as shown in the following procedure.

In this example we will be using uservg as the volume group and userlv as the logical volume. First, determine the mounted file systems:

# mount
node      mounted     mounted over  vfs     date       options
------ -------------- -------------  ---- ----------- --------------
       /dev/hd4       /              jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd2       /usr           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd9var    /var           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd3       /tmp           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd1       /home          jfs  Nov 16 18:46 rw,log=/dev/hd8
       /dev/userlv    /u             jfs  Nov 18 11:25 rw,log=/dev/loglv00

Notice that the log for the /userlv logical volume is the logical volume loglv00.

To check the loglv00 LV enter:

# lslv loglv00
LOGICAL VOLUME: loglv00             VOLUME GROUP: uservg
LV IDENTIFIER:  00091974342f2afa.2  PERMISSION:   read/write
VG STATE:       active/complete     LV STATE:     opened/syncd
TYPE:           jfslog              WRITE VERIFY: off
MAX LPs:        512                 PP SIZE:      8 megabyte(s)
COPIES:         1                   SCHED POLICY: parallel
LPs:            1                   PPs:          1
STALE PPs:      0                   BB POLICY:    relocatable
INTER-POLICY:   minimum             RELOCATABLE:  yes
INTRA-POLICY:   middle              UPPER BOUND:  32
MOUNT POINT:    N/A                 LABEL:        None
MIRROR WRITE CONSISTENCY: on
EACH LP COPY ON A SEPARATE PV ?: yes

Check the physical volumes (PVs) to look for a drive with no VG associated.

# lspv
hdisk0         000919746edab91f    rootvg
hdisk1         0009197459d92f2e    None
hdisk2         00091974d381d097    uservg
hdisk3         00091974d81ff431    uservg
hdisk4         00091974de731316    None

Notice that hdisk1 and ^hdisk4 have no VGs assigned to them. To extend the uservg volume group to incorporate hdisk4 type:

extendvg -f 'uservg' 'hdisk4'

To create the jfslog on hdisk4 enter:

smitty mklv

In Figure 88 , select VOLUME GROUP name. In this example it is uservg.

Figure 88: Add a Logical Volume Menu

From the Add a Logical Volume menu, select the following options:

Logical volume NAME to create

userlog

Number of LOGICAL PARTITIONS: 1
PHYSICAL VOLUME names: hdisk4
Logical volume TYPE: jfslog
POSITION on physical volume: center

as displayed in Figure 89.

Figure 89: Add a Logical Volume Selection Menu

Once completed, the COMMAND STATUS screen will display confirmation as displayed in Figure 90.

Figure 90: Add a Logical Volume Command Status

Press F10 and exit SMIT to the command line and enter the following:

# /usr/sbin/logform /dev/userlog
logform: destroy /dev/userlog (y)?y

Note

The preceding command formats the JFS-log logical volume so that it can record file-system transactions. Nothing is destroyed despite the wording in the prompt.

Note
The preceding command formats the JFS-log logical volume so that it can record file-system transactions. Nothing is destroyed despite the wording in the prompt.

Make sure the /userlv has been mounted by typing:

# mount
node      mounted     mounted over  vfs     date       options
------ -------------- -------------  ---- ----------- --------------
       /dev/hd4       /              jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd2       /usr           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd9var    /var           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd3       /tmp           jfs  Nov 16 18:45 rw,log=/dev/hd8
       /dev/hd1       /home          jfs  Nov 16 18:46 rw,log=/dev/hd8
       /dev/userlv    /u             jfs  Nov 18 11:25 rw,log=/dev/userlog

Notice that the log is now userlog instead of loglv00.

To verify that you have set up the file system and log correctly, use the following command:

# lsvg -l uservg
uservg:
LV NAME          TYPE    LPs  PPs  PVs  LV STATE    MOUNT POINT
userlv           jfs     820  820  2    open/syncd  /u
userlog          jfslog  1    1    1    open/syncd  N/A#

There should be two logical volumes listed, as shown in the preceding example.

5.6 Troubleshooting File System Problems