HP 3000 Manuals HP 3000 Manuals
Introducing the New DIRLIMIT Utility
by Joanne Gong
Computer Systems Division
Functionality
A new utility DIRLIMIT is introduced in the MPE/iX Release 5.0. This
utility allows system managers to configure a maximum directory size for
all the directories on the system. At the system bootup time, the MPE/iX
Operating System sets the default directory size limit to the maximum
file size allowed by the File System. After the system is up, the system
manager can run this utility to alter the directory size limit. The
rationale of limiting the directory size is to prevent possible
system performance degradation and catastrophic failures due to an
extraordinarily large directory.
DIRLIMIT utility can be run any time after the system is booted and as
frequently as needed. The limit is defined as maximum bytes allowed for
any directory in a system. Since each directory type has a different
record size, a fixed byte limit on all the directories implies different
entry limits for different directories. Entries in the root directory
take 128 bytes, entries in account directories take 172 bytes, entries in
group directories take 40 bytes, and the entries in Hierarchical File
System directories typically take 96 bytes, but may be larger depending
on the length of the entry name.
Executing the DIRLIMIT program alters a system's directory size limit
immediately. Any future directory growth is restricted by the limit most
recently set. The previous limit is not restricted, but it cannot be
expanded.
For example, inserting a file or creating a new group, account or
directory fails if the directory file being inserted has reached the
system's directory size limit. The directory size limit configured by
the system manager is not retained across system reboots.
Each system reboot resets the directory limit to the File System's
default maximum file size. The system administrator can automate the
execution of the DIRLIMIT program by incorporating it in a batch job
streamed by the SYSSTART file.
The Interface
The DIRLIMIT is a utility program residing in the MPEXL group of the
TELESUP account. The program requires that you have System Manager
capability. It can be invoked by a RUN command:
________________________________________________________________________
|:run DIRLIMIT.MPEXL.TELESUP |
| |
|DIRLIMIT A.01.00 Copyright (C) Hewlett-Packard 1994. All rights |
|reserved. |
| |
|The current directory byte limit is 4294901759 |
|Enter a new limit or hit CR to exit---> 2500000000 |
|The maximum size of directories is set to 2500000000 |
| |
|END OF PROGRAM |
________________________________________________________________________
Invoking the program with a RUN command
If an input parameter is used to invoke the program, you are not prompted
for input:
________________________________________________________________________
|:DIRLIMIT.MPEXL.TELESUP 300000000 |
| |
|DIRLIMIT A.01.00 Copyright (C) Hewlett-Packard 1994. All rights |
|reserved. |
|The maximum size of directories is set to 300000000. |
| |
|END OF PROGRAM |
________________________________________________________________________
Invoking the program with an input parameter
Considerations
What is the appropriate directory size limit to prevent directory
performance problems and system catastrophic failures? There is no
absolute number that can guarantee a risk-free directory size.
Several factors besides the directory size can accelerate the problem:
* Activity level of the system.
* Resource contention situation.
* Type of directory operations--an insertion, deletion or renaming
near the beginning of a directory can cause large amounts of data
to be moved and logged by the Transaction Management.
The decision on the directory size limit should be based on the system
usage. It is assessed that if a system's directory size is limited to
two megabytes, the risk associated with extraordinarily large directories
is lowered to the point that it only occurs in unusual circumstances.
The two megabytes directory size limit equates to the following entry
limits for various directory types:
* 15,625 entries for the root directory
* 11,628 entries per account
* 50,000 entries per group
* Approximate 20,833 entries per HFS directory