The difference between JFS and JFS2

Could you tell me the difference between JFS and JFS2? Support the largest file? General jfs:2g; Support large file jfs:64g;jfs2:1t support the largest file system? Ordinary JFS, how big is it to support large files JFS,JFS2?

The maximum file size and maximum file system size is limited to (1 TB – (physical partition size)) when used with the 32- Bit kernel. For example, if the physical partition size for the volume group is 1 MB, then the maximum MB) = (1048576 MB-64 MB) = 1048512 MB. This was due to an underlying limitation on the maximum size of a logical volume when using the 32-bit kernel.

JFS2 Size Limits
Testing has shown so extremely large JFS2 file systems that contain very large files is more practical to maintain than Those that contain a large number of small files. When a large file system contains many small files, the fsck command and other file system maintenance tasks take a long t IME to run. The following size limitations is recommended:maximum JFS2 file system SIZE:32TB (+ bit kernel) 1 TB (32-bit kernel) M Aximum JFS2 file SIZE:16TB (kernel) 1 TB (32-bit kernel) Minimum JFS2 file System SIZE:16MB
JFS2 size Limit

Testing has shown that it is more feasible to maintain a large JFS2 file system with large files than a larger file system that contains a large number of small files. When a large file system contains many small files, it takes a long time to run the fsck command and other file system maintenance tasks.

The following size limits are recommended:

JFS2 file system maximum size:	TB
JFS2 File Maximum size:	TB
Minimum JFS2 file system size:	MB

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JFS Size Limits
The maximum JFS size is defined when the file system is created. The NBPI, fragment size, and allocation group size is 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 a, the file system size is limit to 8 GB (* 224 = 8 GB). JFS supports NBPI values of 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 in allocation group space allocated to the file system. An allocation group can being 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 is called allocation groups. The allocation group size can specified when the file system is created. The allocation group sizes is 8M, 16M, 32M, and 64M. Each allocation group size have an associated NBPI range. The ranges is 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, 1024x768, 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 is addressable by a number from 0 to (228).
JFS size Limit

Defines the maximum JFS size when creating a file system. NBPI, fragment size, and allocation group size are decisive factors in determining the maximum size.

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

JFS restricts all file systems to an index node of up to M (224).

Create an index node for the allocation group space for each NBPI byte assigned to the file system. Although the total number of index nodes for each allocation group is still assigned, one allocation group can be partially assigned. In the file system, NBPI is inversely proportional to the total number of index nodes.

JFS divides the file system space into the grouping of index nodes and disk blocks for user data. These groupings are called allocation groups. You can specify the allocation group size when you create the file system. The allocation group size is 8 m, m, M, and M. Each allocation group size has an associated NBPI range. These scopes 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, 163 32768, 65536 4096, 8192, 16384, 32768, 65536, 131072 JFS supports contiguous disk space for four fragment sizes of 512, 1024, 2048, and 4096 byte units. JFS keeps the number of fragment addresses in index nodes and indirect blocks as 28 digits. Each fragment must be addressable by a number from 0 to (228).

JFS and JFS2 Size limitations You define the maximum size for a JFS when you create the file system. The decision of what size to define for a JFS are based on several significant issues. The following section describes the key considerations. The recommended maximum size for a JFS2 is the TBs. The minimum file system size for a JFS2 is an MBs. Key considerations for very large JFS2 file systems be described in JF S2 size limits. Although file systems, use allocation units smaller than 4096 bytes require substantially less disk space than those u Sing the default allocation unit of 4096 bytes, the use of smaller fragments might incur performance costs. The allocation state of each fragment (JFS) or block (JFS2) within a file system are recorded in the file system allocation Map. More virtual memory and file system disk space might is required to hold allocation maps for file systems with a fragment or block size smaller than 4096 bytes. Because disk space is allocated-smaller units for a file system with a fragment (JFS) or block (JFS2) size other than 4 096 bytes, allocation activity can occur more often when files or directories is repeatedly extended in size. For example, a write operation this extends the size of a zero-length file by a. Bytes results in the allocation of one 5 12-byte fragment or block to the file, depending the file system type. If The file size is extended further by another write of a bytes, an additional fragment or block must being allocated to T He file. Applying this example to a file system with 4096-byte fragments or blocks, disk space allocation occurs only once, as part Of the first write operation. No additional allocation activity must be performed as part of the second write operation since the initial 4096-byte allo Cation is large enough to hold the data added by the second write operation. Allocation activity can be minimized if the files is extended by 4096 bytes at a time. One size-related issue is the size of the file system log. For JFS, the most instances, multiple file systems use a common log configured to is 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 g Roup 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 L OG size might not being sufficient. In either case, the log sizes is scaled upward as the file system size increases. When the size of the log logical volume is changed, the Logform command must being run to reinitialize the log before the new Space can be used. The JFS log is limited to a maximum size of. There is a practical limit to the size of the combined file systems-a single JFS log can support. As a guideline, one trillion bytes of total file system capacity are the recommended limitation for a single JFS log. When this guideline was exceeded or was close to being exceeded, or when out-of-memory errors occur from the Logredo command (which is called by the fsck command), add a additional JFS log and then share the load between the both JFS log files. For JFS2, in the most instances, multiple the file systems also use a common 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 L OG size might not being sufficient. In either case, you can scale log sizes upward as the file system size increases or can add an additional JFS2 log and Then share the load between the JFS2 log files. JFS and JFS2 size limits When you create the file system, you define the maximum size of the JFS. Determine how large a size is to be defined for a JFS based on several important issues. The maximum recommended size for JFS2 is TB. The minimum file system size for JFS2 is MB. Although a file system that uses an allocation unit smaller than 4096 bytes requires significantly less disk space than a file system that uses the default allocation unit of 4096 bytes, using smaller fragments can incur performance costs. The allocation status of each fragment (JFS) or block (JFS2) in the file system is recorded in the file system allocation diagram. Additional virtual memory and file system disk space may be required to hold an allocation diagram for a file system with a fragment or block size less than 4096 bytes. Because disk space is allocated in smaller units for file systems that have a segment (JFS) or block (JFS2) size other than 4096 bytes, the allocation activity may occur more frequently when the file or directory size is repeatedly extended. For example, a write operation that extends a 0-length file by 512 bytes causes a 512-byte fragment or block to be allocated to the file based on the file system type. If another 512-byte write further expands the size of the file, you must assign an additional fragment or block to the file. Apply this example to a file system that has 4096 bytes of fragments or blocks, and disk space allocation will occur only once as part of the first write operation. Since the initial 4096-byte allocation is large enough to hold the data added by the second write operation, no additional allocation activity must be performed as part of the second write operation. If you extend these files by 4096 bytes at a time, you can minimize the allocation activity. One size-related issue is the size of the file system log. For JFS, in most instances, multiple file systems use a public log that is configured to be 4 MB in size. For example, after an initial installation, all file systems in the root volume group use the logical volume HD8 as a public JFS log. The default logical volume partition size is 4 MB, and the default log size is a partition, so the root volume group typically contains a 4 MB JFS log. The default log size may be insufficient when the file system exceeds 2 GB or the total amount of file system space using a single log exceeds 2 GB. Either way, the log size increases with the size of the file system. When the size of a log logical volume changes, you must run the Logform command to reinitialize the journal before you can use the new space. JFS logs are limited to a maximum size of zero MB. There is a real limit to the size of the combined file system that can be supported by a single JFS log. As a benchmark, the recommended limit for a single JFS log is the total file system capacity of trillions (trillion) bytes. When this baseline is exceeded or is about to exceed this baseline, or the Logredo command (called by the fsck command) occurs with an "out of memory" error, an additional JFS log is added and the load is shared between the two JFS log files. For JFS2, in most instances, multiple file systems also use a common log. The default log size may be insufficient when the file system exceeds 2 GB or the total amount of file system space using a single log exceeds 2 GB. Either way, you can increase the log size when the file system size increases, or you can add an additional JFS2 log, and then share the load between the two JFS2 log files.

The difference between JFS and JFS2