AIX File Systems

# File Systems Types:
JFS, EJFS, NFS, CD-ROM File systems

# File Systems Structure:
Superblock: It contains control information about file systems such as a) Size of the file systems b) Name of the file systems c) The System log device d) The version number e) The number of inodes f) List of free inodes and data-bocks g) Date and time of creation of file system and also file system state.
IMP: Corruption of data may render the file system unusable. This is why system keeps a second copy of superblock on logical block 31.Allocation Group: It consists of inodes and it corresponding data blocks. An allocation group spans multiple adjacent disk blocks and it improves the speed of i/o operation. Booth jfs and jfs2 file systems use allocation group.

Inodes: It contains control information about file such as a) Type, Size, Owner, and the date and time when the file was created, modified, last accessed. b) it also contains the pointers to data blocks that store the actual data of file. Every File has a corresponding inode. c) The jfs restricts all file systems to 16 MB inodes.
Data Blocks: It stores the actual data of the file or pointers to other data blocks. Default value for disk block size is 4 kb.
Fragments: Fragments of logical blocks can be used to support files smaller than the standard size of the logical block ( 4 kb ). This rule applies only to last block of a file smaller than 32 kb.

File Systems Differences

Function JFS JFS2
Architectural maximum file system size 1 TB 4 PB
Architectural maximum file size 64 GB 4 PB
No of inodes Fixed, set at Dynamic system creation
Inode size 128 bytes 512 bytes
Fragment size 512 512
Block size 4096 4096
Directory organization Linear B-tree
Compression Yes No
Default ownership at creation sys.sys root.system
SGID of default file mode SGID=on SGID=off

Example of file system creation

Creating file systems without specifying logical volumes
# lsvg -l testvg
testvg:LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINT
# crfs -v jfs -g testvg -a size=10M -m /fs1
Based on the parameters chosen, the new /fs1 JFS file systemis limited to a maximum size of 134217728 (512 byte blocks)New File System size is 262144
# crfs -v jfs2 -g testvg -a size=10M -p ro -m /fs2
File system created successfully.130864 kilobytes total disk space.New File System size is 262144
# lsvg -l testvg
testvg:LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINTloglv00 jfslog 1 1 1 closed/syncd N/Alv00 jfs 1 1 1 closed/syncd /fs1loglv01 jfs2log 1 1 1 closed/syncd N/Afslv00 jfs2 1 1 1 closed/syncd /fs2
# lslv lv00
LOGICAL VOLUME: lv00 VOLUME GROUP: testvgLV IDENTIFIER: 00c478de00004c0000000107d96de510.2 PERMISSION:read/writeVG STATE: active/complete LV STATE: closed/syncdTYPE: jfs WRITE VERIFY: offMAX LPs: 512 PP SIZE: 128 megabyte(s)COPIES: 1 SCHED POLICY: parallelLPs: 1 PPs: 1STALE PPs: 0 BB POLICY: relocatableINTER-POLICY: minimum RELOCATABLE: yesINTRA-POLICY: middle UPPER BOUND: 32MOUNT POINT: /fs1 LABEL: /fs1MIRROR WRITE CONSISTENCY: on/ACTIVEEACH LP COPY ON A SEPARATE PV ?: yesSerialize IO ?: NO
# lslv fslv00
LOGICAL VOLUME: fslv00 VOLUME GROUP: testvgLV IDENTIFIER: 00c478de00004c0000000107d96de510.4 PERMISSION:read/writeVG STATE: active/complete LV STATE: closed/syncdTYPE: jfs2 WRITE VERIFY: offMAX LPs: 512 PP SIZE: 128 megabyte(s)COPIES: 1 SCHED POLICY: parallelLPs: 1 PPs: 1STALE PPs: 0 BB POLICY: relocatableINTER-POLICY: minimum RELOCATABLE: yesINTRA-POLICY: middle UPPER BOUND: 32MOUNT POINT: /fs2 LABEL: /fs2MIRROR WRITE CONSISTENCY: on/ACTIVEEACH LP COPY ON A SEPARATE PV ?: yesSerialize IO ?: NO
# cat /etc/filesystemsgrep -ip fs1
/fs1:dev = /dev/lv00 vfs = jfslog = /dev/loglv00mount = falseaccount = false
# mount -a (Mount all the file systems)
# mount (Display mounted file systems)
# lsfs (Shows the characteristics of a file systems)
# rmfs (Removes the file systems)

Removing the file Systems

# rmfs /test
rmfs: 0506-921 /test is currently mounted.
# umount /test
# rmfs /test
rmlv: Logical volume testlv is removed.
# lsvg -l testvg
testvg:LV NAME TYPE LPs PPs PVs LV STATE MOUNT POINTloglv00 jfslog 1 1 1 closed/syncd N/Alv00 jfs 1 1 1 closed/syncd /fs1loglv01 jfs2log 1 1 1 closed/syncd N/Afslv00 jfs2 1 1 1 closed/syncd /fs2
# cat /etc/filesystemsgrep test#

Changing the attributes of file systems

# chfs -a size=250M -p rw /fs2

Filesystem size changed to 524288
# fsck(Checks the Systems consistency and interactively repairs the file systems. Always run the fsck command on the mounted file systems.)

If First super block corrupted then how to recover

If you receive one of the following errors from the fsck or mount commands, the problem may be a corrupted superblock:
fsck: Not an AIX3 file systemfsck: Not an AIXV3 file systemfsck: Not an AIX4 file systemfsck: Not an AIXV4 file systemfsck: Not a recognized file system typemount: invalid argument
The problem can be resolved by restoring the backup of the superblock over the primary superblock using one of the following commands:
# dd count=1 bs=4k skip=31 seek=1 if=/dev/lv00 of=/dev/lv00

Not able to umount the file systems

Files are open within a file system. Close these files before the file system can be unmounted. The fuser command is often the best way to determine the process IDs for all processes that have open references within a specified file system. The process having an open reference can be killed by using the kill command and the unmount can be accomplished.
If the file system is still busy and not getting unmounted, this could be due to a kernel extension that is loaded, but exists within the source file system. The fuser command will not show these kinds of references, because a user process is not involved. However, the genkex command will report on all loaded kernel extensions.
# find /home -type d -exec fuser -u {} \;/home:/home/lost+found:/home/guest:/home/kenzie: 3548c(kenzie)