JFS and Minfree

[Valkiria Santos]

I create a vxfs file system, when I execute df -t minfree displayed its 0 percent. My application need likes a 1 percent. Its possible set minfree or is this dynamic in vxfs?

[James R. Ferguson]

Hi:

Document #UNX1030055 states:

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How do I set minfree on JFS?

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Score : 67
Document Type : EN
Date : 1997 Aug 25
Description : How do I set minfree on JFS?
Document Id : UNX1030055
Search String : minfree

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Problem Description

How do I set minfree on JFS?

Solution

The minfree for JFS is set at approximately 10 percent (10%) and is calculated by the following formula:

minfree = (number-of-file-system-data-blocks / 100 ) * 10

This is not tunable for JFS. To balance JFS file system usage, JFS will stop allocating very large extents when the file system free space falls below minfree.

The HP OnLineJFS product, a separately orderable product, supports reorganizing directories and extents to reduce fragmentation and wasted space. The system administrator can use fsadm(1M) to perform this
reorganization. Refer to the fsadm_vxfs(1M) man page for more information.

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...JRF...

[Denver Osborn]

I think JFS 3.3 offers a vxtunefs command to adjust vfs parameters. Not sure if minfree is one of them though, I'd have to look into it.

[Worapoj P.]

Dear all

Also on my system(hpux 11.0 on N4000) some of file system shown "0 percent minfree" , what dose it mean? look like that file system has
full(not extend anymore) or not? but it still has free space for extend files or directories


Thanks advance for explaination,
Worapoj P.

[Wieslaw Krajewski]

Hi,

I've tried some experiments with minfree for JFS.
I've observed:

1. For new vxfs minfree was equal to 6%, only for a very small file system minfree = 5%.

2. When creating new files in this file system, i.e. when available space was decreasing the value of minfree was going going to 0%. but I haven't notice any impact on a possibility of extending existing files or possibility of creating new ones.

3. Do not remember at what value of available space minfree became equal to 0, bur definitely there is space available when minfree reach 0%.

4. This allows to conclude that for JFS minfree changes dynamically.

5. As concerns reservation a room for application, if you have On Line JFS you can use setext command which allows to reserve space for a file.

Hope this helps a little.