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JFS.IFS Frequently Asked Questions

   Q1: What is JFS filesystem?
*  Q2: Can I use Bootable JFS on SCSI disk?
*  Q3: Does eComStation use JFS or JFS2?
*  Q4: My PC hangs when coping files to/from JFS volume
   Q5: Can I use JFS filesystem on USBMSD devices? 
   Q7: Can chkdsk intensify the state of damaged JFS volume?
   Q9: Which value of /CACHE:x  to use for JFS.IFS?
  Q10: Chkdsk returns error JFS0138
  Q13: Trap 3.
* Q14: How to read/write JFS volume from Windows?
* Q15: How to read/write eComStation JFS volume from Linux?
  Q16: How many disk space the .LONGNAME requires?
  Q17: Can I use Defragfs.exe for JFS?    
  Q25: Why the size of swap file on JFS can't exceed 2 Gb?
  Q28: How to prevent data loss? 
  Q29: JFS Lazywrite parameters in CONFIG.SYS
* Q30: Chkdsk returns error JFS0148
* Q31: Does Bootable JFS work with AirBoot bootmanager?

Q4: My PC hangs/traps when coping files to/from JFS volume
A4: Usually the hang/trap happens because of cross-linked/damaged structures/files. Boot from eCS CD, check the JFS volume:
chkdsk x: /f

C-ENG-JFS-1210, 2009/08/08

Q5: Can I use JFS filesystem on USBMSD devices?
A5: Yes you can format flash cards as JFS if using JFS for eComStation (JFS package released in 2005 or later via eCS beta-zone). Attention: if you are using lazywrite (/LW:ON) then eject x: command may require some minutes. Don't disconnect device while eject! Example: if using an old flash-card actively and then write big file (128 Mb), the eject will require more than 10 minutes.

Q7: Can chkdsk intensify the state of damaged JFS volume?
A7: Chkdsk may correct the volume so JRescuer fails on recover. Nevertheless the data may be saved with additional efforts.

Q9: Which value of /CACHE:x to use for JFS.IFS?
A9: The size of cache is measured in KBytes. You can use 4 Mb .. 200 Mb (4096 .. 204800) There is no point in setting less than 20 Mb for JFS cache.

C-ENG-JFS-0794

Q10: Chkdsk returns error JFS0138
A10: It's normal. Every mounted drive is "abnormal" for chkdsk.

Q13: Trap 3. Validfs.exe runned after chkdsk /f doesn't report that "fs is valid". It reports which inodes have violation in structure.
A13: Determine the name of file using JRescuer. Save it, remove old one. Continue until Validfs informs that "fs is valid"

Q14: How to read/write JFS volume from Windows?
A14: There is not JFS filesystem driver for Windows.

C-ENG-JFS-1205, 2008/09/02

Q15: How to read/write eComStation JFS volume from Linux?
A15: No guarantees that it will work, that your data will survive. Access JFS from Linux:

• try set uid, gid equal to 0
• rights = empty
• iocharset=cp866 (useful for russian users)

C-ENG-JFS-1206, 2008/09/02

Q16: How many disk space the .LONGNAME requires?
A16: An inode occupies one cluster per file/directory. The default size of cluster is 4096 bytes. The size of inode itself is 512 bytes. So, there is space 4096-512 bytes for EA and ACC. The max length of LONGNAME is 255 bytes.

As you can see, the .LONGNAME attribute requies additional:

          0 bytes -- if file doesn't have EA attributes,
          0 or 1 cluster -- if file has EA but doesn't have .LONGNAME 

Q17: Can I use Defragfs.exe for JFS?
A17: Don't use it. It is dangerous.

C-ENG-JFS-0796

Q25: Why the size of swap file on JFS can't exceed 2 Gb?
A25: Research the VIRTUALADDRESSLIMIT= line in CONFIG.SYS If you need bigger swap file then set value greater than 2048

C-ENG-JFS-0795

Q28: How to avoid data loss?
A28: Some suggestions:

• Don't create composite (spanned) JFS volumes. JRescuer doesn't support spanned volumes.
• Make sure that GenMac works fine for you (some users blame JFS after they have lost data while copying via GenMac networking)

C-ENG-JFS-810-2008/05/05??

Q29: JFS Lazywrite parameters in CONFIG.SYS
A29: The parameters for the Journaled File System (JFS) installable file system are as follows:

         IFS=jfs.ifs /L:OFF
         IFS=jfs.ifs /L:synctime,maxage,bufferidle
     JFS ignores any characters between the L (or l) and the colon; valid 
     flags are /L: /LAZY: /LW: /lazywrite: and so on.
     
       OFF - Forces asynchronous writes to be immediately initiated.
  Synctime - The interval at which the synchronous thread runs. 
             The default is 64. 
    maxage - The longest time that a frequently-modified file is kept in 
             cache. The default is synctime*4.
bufferidle - The time indicating a recent change. Changes newer than this 
             value are not written unless the last write was older than 
             maxage. The default is MIN(1,synctime/8)

Note: All parameters are in seconds.

The following are some usage examples:

IFS=C:\OS2\JFS.IFS /L:64
synctime = 32, maxage = 128, bufferidle = 4 
IFS=C:\OS2\JFS.IFS /LW:10,60,5 synctime = 10, maxage = 60, bufferidle = 5 
IFS=C:\OS2\JFS.IFS /LAZYWRITE:4,60
synctime = 4, maxage = 60, bufferidle = 1
IFS=C:\OS2\JFS.IFS /lazy:off
All writes initiated immediately (synctime=1, maxage=bufferidle=0)

Note: The synchrounous thread still runs since things like marking an inode accessed are still deferred.

The CACHEJFS.EXE command allows the lazywrite parameters to be changed immediately. The syntax is similar 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

C-ENG-JFS-0312, 2008/01/19

Q30: Chkdsk returns error JFS0148
A30: Replace harddisk, this one is going to die.

C-ENG-JFS-1202, 2009/05/08

Q31: Does Bootable JFS work with AirBoot bootmanager?
A31: Yes, please use AirBoot 1.0.4 and higher.

C-ENG-JFS-1201, 2009/05/09