JFS size limits

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The maximum JFS size is defined when the file system is created. The NBPI, fragment size, and allocation group size are contributing factors to the decision.

The file system size limitation is the minimum of the following: 
NBPI * 224
or 
FragmentSize * 228
For example, if you select an NBPI ratio of 512, the file system size is limit to 8 GB (512 * 224 = 8 GB). JFS supports NBPI values of 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, and 131072.

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

One i-node is created for every NBPI bytes of allocation group space allocated to the file system. An allocation group can be partially allocated, though the full number of i-nodes per allocation group is still allocated. NBPI is inversely proportional to the total number of i-nodes in a file system.

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 8M, 16M, 32M, and 64M. Each allocation group size has an associated NBPI range. The ranges are defined by the following table:

Allocation Group
Size in Megabytes      Allowable NBPI Values
 8                     512, 1024, 2048, 4096, 8192, 16384 
16                          1024, 2048, 4096, 8192, 16384, 32768 
32                                2048, 4096, 8192, 16384, 32768, 65536 
64                                      4096, 8192, 16384, 32768, 65536, 131072

The JFS supports four fragment sizes of 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).