Summary: Largest Contiguous Space Available

From: Mark Hargrave (
Date: Thu Apr 09 1998 - 12:35:29 CDT

Thanks to all who responded!

Here is the original question and some of the replies:

Original Question:

Is there a command that will tell me what the largest
contiguous space is available on a given file system?

Our DBA people need to know this in support of Oracle.

For example, they want to know if they can create a
200 MB contiguous file.


One way is to copy/save the filesystem out to tape or another disk -
delete all files on that old disk filesystem, then copy the data back
from the tape or disk save. Then run df -k.

From: Eugene Kramer <

I do not know the direct answer. Indirect would be:
        - dump FS
        - newfs
        - allocate space for Oracle
        - do not put anything else there :-)

From: Stephen Harris <>

With Oracle, the number of physical disks and controllers have a much
larger effect on Oracle performance than the continuity of the disk blocks.

Finally, note that Oracle does not need disk files to be mapped contiguously
onto a filesystem.

From: Ed Finch <efinch@eos.EAST.HITC.COM>

The ufs filesystems is substantially different from FAT. Among the

- Space is never allocated contigually
- It gets fragmented, but rarely above a few %
- It reserves 10% of the available space (by default) for performance
reasons and, historically, to always enable root to login.

As an aside, most DB vendors such at Oracle and Sybase recommend raw
disk partitions for the the databases. This avoids the ufs filesystem
altogether (since it isn't needed) and provides better performance.

From: (Peter L. Wargo)

Sure: mkfile 200m <filename> - AFAIN, it's all contiguous... (Remember
the beauty of the UNIX filesystem? Virtually no fragmentation....)

We've had no problem with cooked or raw stuff, under oracle or sybase.


I would highly recommnd getting vxfs,which is extent basedf for just
such as this.

From: "Wozniak Chris" <>

What for ??
Oracle doesn't bother about system's data file being contiguos or not, that's
taken care of by the ufs.

From: Dennis Martens <>

I was of the opinion that, because a file system is split into separate
cylinder groups, 'contiguous space' was not really much of an issue with

I used to use a command called 'dumpfs' under SunOS, it was used in
conjunction with 'tunefs'. Under Solaris, 'tunefs' still exists, but
'dumpfs' does not. It may have been able to tell you about contiguous

Jim Robertori <>

With Oracle, I always thought you were better off using a raw partition.



Mark Hargrave, Sr. Unix Systems Manager
Lockheed Martin Michoud Space Systems
New Orleans, LA


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