Differences Between JFS and JFS2

Introduction About Journaled File Systems:

Journaled File Systems LOG is used to stores transactional information about file system metadata changes and can be used to roll back incomplete operations if the machine crashes  That's why log devices should always be protected by mirroring or raid 0+1 or raid 5 

You cannot see files associate with jfslog devices because they're not mounted over any File Systems  They're raw devices used by Logical Volumen Manager (LVM) to keep information about changes in metadata  You can create a jfslog device and format it (destructive operation) and assign to any JFS, even more, you can assign the same jfslog more than one JFS  You can create a jfslog type 2 to log metadata for JFS2 File Systems or use the new INLINE log device for JFS2 only 

DIFFERENCES BETWEEN JFS AND ENHANCED JFS(JFS2):

There are many differences between JFS and Enhanced JFS.

Table 1. Functional Differences between JFS and Enhanced JFS

Function                                                   JFS                                              Enhanced JFS

Optimization                                        32-bit kernel                                     64-bit kernel

Maximum file system size                  32 terabyte                                        4 petabytes

Note: This is an architectural limit. AIX® currently only supports up to 16 terabytes.

Maximum file size                              64 gigabytes                                       4 petabytes

Note: This is an architectural limit. AIX currently only supports up to 16 terabytes.

Number of I-nodes                        Fixed at file system creation       Dynamic, limited by disk space

Large file support                             As mount option                                 Default

Online defragmentation                            Yes                                                 Yes

namefs                                                       Yes                                                Yes

DMAPI                                                    No                                                  Yes

Compression     Yes         No

Quotas                 Yes         Yes

Deferred update              Yes         No

Direct I/O support           Yes         Yes