what is filesystem?
A filesystem is a set of files ,directories and other structures.
filesystem maintains information and identify the location of a file or directory's data .
it may also contain a boot block, a superblock ,bitmaps and one or more allocation groups.
*allocation group contains disk i-nodes and fragments.
filesystem supported by aix
1. JFS(journaled filesystem)
2. JFS2(enhanced journaled filesystem)
3. NFS(network filesystem)
4. CDRFS(cd-rom filesystem)
JFS
it uses database journaling techniques, such as recording file changes sequentially, to a mintain the integrity of control structure.
each journaled filesysten resides on distint jfs logical volume
JFS2
it uses extent based allocation to allow higher performance,larger filesystem and larger file-size.
each enhanced journaled filesystem must reside on a distinct JFS2 logical volume.
when aix is installed using default option ,it creates JFS2 filesystem.
NFS
it is distributed filesystem that allows users to access files and directories located on remote computers and use those files and directories as they are local.
CDRFS
this filesystem allows you to access the content of CD-ROM through the normal filesystem interfaces.
filesystem structure
journaled file-system uses following data structures:
1.) superblock
2.) allocation group
3.) inodes
4.) blocks
5.) fragments
6.) device logs
superblock
super block contains controlinformation aboyt a filesyatem such as
1. overall size of file-system in 512 byte blocks
2. file-system name
3. file-system log device
4. version no.
5. no. of inodes
6. list of free inodes,free blocks
7. date and time of creation
8. file-system state
corruption of super-block may lead the filesystem to become un-usable.
***the system keeps a second copy of the super-block on logical block 31.
allocation group
An allocation group consists of inodes and its correspondong data blocks.
An allocation group spans multiple adjacentdisk blocks and improves the speed of i/o operations
inode
inode contains control information about the file .it contains following details of files
1. type
2. size
3. owner
4. date and time of creation
5. last accessed
6. a pointer to block that stores the actual data
# istat /abhi/aks
data block
data block stores the actual data of the file or pointers to another data block
device logs
the jfs log stores transactional information about filesystem metadata changes. this data can be used to roll back incomplete operations if the machine crashes.
*filesystem used for logging is of type "jfs2log"
in aix, hd8 is the common log
things you must know
/root - it is root user home directory.
/home - here all users that you have created will be stored.
/bin - it contains executable binaries that any user can run.
/sbin - it contains the executable binaries that only admin or root user can run.
/etc - it contains all the configuration files. like files related to DNS ,DHCP configuration etc
/dev - as we know that in unix everything is file. so, all devices that are defined in aix will have one
file in this directory.
/tmp - it contains all the temporary files.
/var - it contains all the log files
A filesystem is a set of files ,directories and other structures.
filesystem maintains information and identify the location of a file or directory's data .
it may also contain a boot block, a superblock ,bitmaps and one or more allocation groups.
*allocation group contains disk i-nodes and fragments.
filesystem supported by aix
1. JFS(journaled filesystem)
2. JFS2(enhanced journaled filesystem)
3. NFS(network filesystem)
4. CDRFS(cd-rom filesystem)
JFS
it uses database journaling techniques, such as recording file changes sequentially, to a mintain the integrity of control structure.
each journaled filesysten resides on distint jfs logical volume
JFS2
it uses extent based allocation to allow higher performance,larger filesystem and larger file-size.
each enhanced journaled filesystem must reside on a distinct JFS2 logical volume.
when aix is installed using default option ,it creates JFS2 filesystem.
NFS
it is distributed filesystem that allows users to access files and directories located on remote computers and use those files and directories as they are local.
CDRFS
this filesystem allows you to access the content of CD-ROM through the normal filesystem interfaces.
filesystem structure
journaled file-system uses following data structures:
1.) superblock
2.) allocation group
3.) inodes
4.) blocks
5.) fragments
6.) device logs
superblock
super block contains controlinformation aboyt a filesyatem such as
1. overall size of file-system in 512 byte blocks
2. file-system name
3. file-system log device
4. version no.
5. no. of inodes
6. list of free inodes,free blocks
7. date and time of creation
8. file-system state
corruption of super-block may lead the filesystem to become un-usable.
***the system keeps a second copy of the super-block on logical block 31.
allocation group
An allocation group consists of inodes and its correspondong data blocks.
An allocation group spans multiple adjacentdisk blocks and improves the speed of i/o operations
inode
inode contains control information about the file .it contains following details of files
1. type
2. size
3. owner
4. date and time of creation
5. last accessed
6. a pointer to block that stores the actual data
# istat /abhi/aks
data block
data block stores the actual data of the file or pointers to another data block
device logs
the jfs log stores transactional information about filesystem metadata changes. this data can be used to roll back incomplete operations if the machine crashes.
*filesystem used for logging is of type "jfs2log"
in aix, hd8 is the common log
things you must know
/root - it is root user home directory.
/home - here all users that you have created will be stored.
/bin - it contains executable binaries that any user can run.
/sbin - it contains the executable binaries that only admin or root user can run.
/etc - it contains all the configuration files. like files related to DNS ,DHCP configuration etc
/dev - as we know that in unix everything is file. so, all devices that are defined in aix will have one
file in this directory.
/tmp - it contains all the temporary files.
/var - it contains all the log files
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