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JFS.IFS (CONFIG.SYS)

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OS/2 Warp Server for e-business includes a new file system, the Journaling File System. This new file system is a file system available with IBM's AIX premier UNIX-type operating system. What it offers, among other things, is the ability to manage volumes that exceed the space on one hard disk. For instance, a volume may consist of pieces from one or more physical hard disks which are seamlessly integrated into one volume. In addition to being able to set up very large volumes, a volume can be expanded at any time so it is larger than it was in real time. 

IFS=JFS.IFS <parameters>

Parameter:

  • /CACHE:

Specifies the size of the JFS buffer cache in Kilobytes. By default, this size is set to 12.5 percent of real memory.

  • /AUTOCHECK:drive[drive...]

Specifies a list of JFS file systems, identified by driver letter, to be included in automatic recovery by CHKDSK at the time of JFS initialization. If an asterisk (*) is specified instead of a drive letter list, all JFS file systems will be included in automatic recovery during JFS initialization. If any drive letter is preceded by an arithmetic plus sign (+), CHKDSK will perform a full integrity check on the drive even if journal log replay has restored the drive to an apparently consistent state. If the list of drive letters ends with plus-asterisk (+*), CHKDSK will perform a full integrity check on all JFS file systems not specified in the list even if journal log replay has restored them to an apparently consistent state.

  • /AC:drives

The AC parameter specifies which drives should be checked by chkdsk.exe during start up after an improper shut down. Add only the drive letter without the colon. If you want to run chkdsk.exe on a drive at every start up add a plus sign (+) in front of the drive letter (undocumented for JFS.IFS).

  • /F:level

Indicates on which level chkdsk.exe should be run. Level can be in the range from 1 to 3 . Default is 2 (undocumented for JFS.IFS).

  • /Force

With this option set you can get access to a disk that is marked as bad and is not in the Autocheck list (the /AC: parameter). But beware there are may errors in the file system, so run chkdsk as soon as possible (undocumented for JFS.IFS).

  • /L:OFF

Specifies the lazy write parameters in seconds. OFF forces all to be synchronous. (JFS ignores any characters between the L (or l) and the colon, so valid flags are /L: /LAZY: /LW: /lazywrite: etc.)

  • /L:

Synctime is the interval at which the sync thread runs, default is 64. Maxage is the longest time that a modified file is kept in cache, default is synctime*4. Bufferidle is the time indicating a "recent" change. Changes newer than this value are not written unless the last write was older than maxage, default is Min(1, synctime/8).

The cachejfs.exe command allows the lazywrite parameters to be changed immediately. The syntax is to the IFS line, except that the /L: prefix is optional. In addition, the cachejfs command can modify the minimum and maximum number of free cache buffers to be maintained. Calling cachejfs with no parameters reports the current settings.

CACHEJFS [[/LAZYWRITE:]{OFF|syncTime[,maxAge[,bufferIdle]]}] /MINFREE:minfree /MAXFREE:maxfree

Because JFS allows fragmentation, a utility, DEFRAGFS, is included with JFS. All these abilities are enabled when formatting a volume with the FORMAT command. The below is the output of a "FORMAT /?" command.

FORMAT drive [/ONCE][/4][/T:tracks][/N:sectors][/F:xxxx][/FS:xxxxx][/L][/V[:label]][/BS:blocksize][/LS:logsize][/S]

Parameter: drive Specifies the drive to be formatted.

  • /ONCE

Specifies that only 1 disk, diskette, or disc is to be formatted and no prompt is to be displayed.

  • /4

Formats a 360KB diskette in a 1.2MB drive.

  • /T:tracks

Specifies the number of tracks per disk side.

  • /N:sectors

Specifies the number of sectors per track.

  • /F:xxxx

Specifies the size to which the diskette is to be formatted. For example: 360, 720, 1.2, 1.44, 2.88.

  • /FS:xxxxx

Specifies the file system to use to format the disk. For example: FS:FAT or FS:HPFS or FS:JFS.

  • /L

Specifies long format procedure for optical read-write disks.

  • /V:label

Specifies the volume label.

  • /BS:blocksize

Specifies, in bytes, the block size desired for the file system. For JFS 512 bytes, 1024, 2048, or 4096 bytes are valid.

  • /LS:logsize

Specifies, in megabytes, the size journal log to create for the file system.

  • /S

Specifies that files on the device will be sparse files. JFS has two file allocation schemes, these being "sparse" and "dense." Sparse allocation is the amount of space allocated to a random-access file when a block written may not be within the earliest portion of a file. Dense allocation allocates all the space prior to the block being written when the block is written. For instance, if a random-access file has 5120 bytes (ten 512 byte blocks), and the fifth block is written to, the resulting usage with sparse allocation is 512 bytes. With dense, the resulting usage will be 2550 bytes, even though the first 2048 bytes are not yet being used. The sparse method is server efficient; only the space used is allocated to the file but this would presumably lead to fragmentation, since when another block is written, the sparse allocation will cause the data to not be in sequentially ordered sectors.

JFS is a very powerful addition to OS/2; it eliminates any limiting factors and make OS/2 Warp Server the best option for serving files, and applications. A file size can be two (2) terabytes (two thousand gigabytes), the maximum volume size. This, along with OS/2 Warp Server's ability to extend beyond just one processor by using up to 64 processors, makes OS/2 Warp Server the most advanced operating system of its kind for the Intel processor.

LVM.EXE is the new version of the FDISK command. It provides both logical and physical views of the hardfiles installed on the system. With LVM (Logical Volume Manager), users can

  • Create Compatibility Volumes (partitions) which can be seen by pre-LVM releases of OS/2
  • Create or delete Logical Volumes which span physical disks
  • Extend file systems (JFS only)
  • Delete Compatibility Volumes (partitions)
  • Recover read or write failures from a portion of the disk going bad (JFS only)

ATTENTION: FDISK is no longer usable for managing partitions once the LVM has been used to create JVS Volumes.

NOTE: OS/2 needs for booting a HPFS or a FAT (better not) partition it can't boot from JFS.

NOTE: JFS is also availabel.for Linux. To create an OS/2 compatible partition use the -O paramter. Format 3rd partition on 2nd hard disk with the volume label "JFS_hdb3" and OS/2 compatibilty: 

mkfs.jfs -L -O JFS_hdb3 /dev/hdb3

Parameter for mkfs.jfs:

  • -c Check the device for bad blocks before building the file system.
  • -j journal_device Set the journal device. (Experimental)
  • -L volume_label Set the volume label for the file system.
  • -O Provide case-insensitive support for compatibility with OS/2.
  • -q Quiet execution - do not ask for confirmation before creating the file system.
  • -s log_size Set the log size (in megabytes). If the -s option is not used, the default is 0.4% of the aggregate size.
  • -V Print version information and exit (regardless of any other chosen options).
Platform Support:
OS/2 2.x OS/2 3.0 OS/2 4.0 OS/2 4.5x
No No No Yes
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