12-10-2003
I don't know aix, but I took a quick look at some web sites and it looks like aix is using an upgraded version of the McKusick filesystem. So I'll take a quick stab at some of this...
NBPI
An inode is a thing that you need to create a file. If a filesystem has 1000 inodes, then it can have 1,000 files. You want to have too many inodes. When you run out of disk space, you will have some unused inodes. That is better than unused disk space with no inodes left to use it. NBPI is number of bytes per inode. Think of it as the average expected file size. By having a default expressed this way, if the filesystem doubles, so do the inodes.
Allocation Group
A filesystem is big so it get chopped up into a few sections called allocation groups. Think about a file that is growing...it needs another data block. You don't want any data block, you want one close by. So the system tries to keep the file in the same allocation group. In fact it tries to keep all of the files in a directory (not subdirectory) in the same allocation unit. Allocation units should be large enough for this to be possible most of the time.
allocation unit
This is the smallest piece of data that can be assigned to a file. A one byte file will use one allocation unit.
That's a quick rundown of these terms. But if you don't understand them all, just take the default values for everything.
Note to freaked out file system gurus...I know that I'm over-simplifying. I think that's what the OP wanted.
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newfs(8) System Manager's Manual newfs(8)
Name
newfs - construct a new file system
Syntax
/etc/newfs [ -N ] [ -n ] [ -v ] [ mkfs-options ] special disk-type
Description
The command is a front-end to the program. The program looks up the type of disk a file system is being created on in the disk description
file calculates the appropriate parameters to use in calling then builds the file system by forking If the file system is a root partition,
installs the necessary bootstrap program in the initial 16 sectors of the device.
If there is no disk description for the specified disk type in the file, the program will use the subroutine to derive disk geometry infor-
mation from the controlling device driver. This functionality is provided for MSCP and SCSI disks.
Options
-N Runs in no update mode. In this mode, will not write to
-n Prevents the bootstrap program from being installed.
-v Instructs to print out its actions, including the parameters passed to
Options which may be used to override default parameters passed to are:
-s size The size of the file system in sectors.
-b block-size
The block size of the file system in bytes.
-f frag-size
The fragment size of the file system in bytes.
-t #tracks/cylinder
-c #cylinders/group
The number of cylinders per cylinder group in a file system. The default value used is 16.
-m free space %
The percentage of space reserved from normal users; the minimum free space threshold. The default value used is 10%.
-o optimization
Specifies whether the file system will optimize for space or for time.
-r revolutions/minute
The speed of the disk in revolutions per minute (normally 3600).
-S sector-size
The size of a sector in bytes (almost never anything but 512).
-i number of bytes per inode
This specifies the density of inodes in the file system. The default is to create an inode for each 2048 bytes of data space.
If fewer inodes are desired, a larger number should be used; to create more inodes a smaller number should be given.
Files
For disk geometry and file system partition information
To actually build the file system
For boot strapping program
See Also
disktab(5), fs(5), chpt(8), fsck(8), format(8v), creatediskbyname(3x), mkfs(8), tunefs(8)
"A Fast File System for UNIX", Supplementary Documents, Volume 3: System Manager
newfs(8)