From: pSeries AIX Geek (aixgeek@YAHOO.COM)
Date: Fri Dec 20 2002 - 23:56:52 EST
Has anyone seen this before? We found that this fixed
some strange file system caching problems on file
systems that contained a large amount of TIF files.
Another undocumented option...
- pAG
Recovery From ENOMEM Error When Copying Files Larger
Than 32K
This document explains the error number 12, ENOMEM (no
memory) problem, the 'mind' option with the mount
command, and information regarding the cause of the
error.
o Environment
o Background
o The problem and the solution
o Recommended fixes
-------------------------------------------------------
Environment
APAR IY13763 was created to correct the error and is
intended for JFS only and no other filesystem types
(JFS2, AFS, GPFS, etc). This fix applies to
Standard/Large/Compressed JFS types on systems running
AIX 4.3.3. At AIX 5.1 JFS and JFS2 filesystems by
default are not affected by this problem.
-------------------------------------------------------
Background
Here is a brief overview of the journaled file system
geometry:
o JFS uses direct, single indirect, and double
indirect disk addressing. The disk inode contains 9
slots for disk addresses. The first 8 are used for the
direct addressing, while the ninth is used for
indirect addressing.
o Direct addressing
If the file is les than or equal to 32K, then the
file will use direct addressing, which means the inode
will point directly to the data blocks.
o Single Indirect addressing
If the file is too larger for direct addressing,
it will use a form of indirect addressing. Single
indirect addressing is called when the file's data
blocks can be addressed by a single indirect block. In
this case, the direct block addresses are unused and
the indirect block address contains the disk address
of the one and only indirect block. Each 4 byte entry
in the indrect block refers to a data block;
therefore, single indirect addressing is used for
files greater than 32K yet less than 4MB.
o Double Indirect addressing
If the file is larger than 4 MB, double indirect
addressing is used. In this case, the indirect field
contains the block number of the double indirect block
for the file. The double indirect block contains 512
pointers to the indirect blocks. As stated before,
each indirect block contains 1024 block addresses for
the data for the file.
For more in-depth coverage of this subject, the
following IBM publications are recommended:
- AIX Logical Volume Manager, from A to Z:
Introduction and Concepts
- AIX V4 documentation library
-------------------------------------------------------
The problem and the solution
The problem with the ENOMEM error occurs when the
system has reached an architectural limit in AIX. The
data read from the indirect blocks of the filesystem
are cached in an indirect segment of virtual memory.
Once the indirect data has been cached, it remains in
virtual memory until the filesystem is unmounted. Once
this segment is full, there is no more room to cache
data and the result is the 'out of memory' error
message.
Note that the problem is with the indirect data and
since a file that is less than 32K does not use
indirect blocks, these smaller files are not affected
by the problem.
A temporary work-around for this problem is unmounting
and remounting the filesystem, which clears out the
.indirect cache. Here are the procedures for
correcting the problem: APAR IY13763 (orginally
IY11431) increases the number of 256MB indirect
segments from one to eight. If this isn't already
applied to the system, it can either be downloaded
from AIX Fix Distribution Service website or ordered.
First check to see if you may already have this APAR
installed.
# instfix -ik IY13763
If it is there you will receive the informational
message:
All filesets for IY13763 were found
If you do receive this message, proceed with the
procedures provided below. If you do not receive this
message, first apply the fix and then complete the
following steps for the filesystem(s) affected:
1.
# umount /fsname
2.
# chfs -a options=rw,mind /fsname
This step will not only update /etc/filesystems,
but will place the information in the LVCB (logical
volume control block). The "mind" (Multi INDirect)
option, will allow that filesystem to use the eight
.indirect segments instead of one.
3.
# mount /fsname
4. Verify the filesystem is mounted with the correct
options:
# mount
You should see something similar to the
following:
/dev/lvname /fsname jfs Jun 27 14:40
rw,mind,log=/dev/loglv05
Other than implementing these procedures, updating the
operating system to 5.1 is the only other option.
-------------------------------------------------------
Recommended fixes
APAR DESCRIPTION AIX LEVEL
IY13763 MULTI-SEGMENT .INDIRECT FOR JFS 4.3.3.
__________________________________________________
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