jfs overhead 1

[Mag0007]

when increasing the filesystem size using chfs, what is the overhead I should expect on a JFS filesystem?

Ie. Increasing 10 gigs on a 120GB partition....

 

[hirschaj]

JFS filesystem seems to have about 4% overhead as far as space is concerned.


Jim Hirschauer

http://www.aixexpert.com

 

[Mag0007]

hirshaj:

thanks! I am not questioning your answer, but how did you find that out? is the 4% of 1meg, 1 gig?

 

[hirschaj]

First off, 4% is 4% no matter what it is applied to When you build a new JFS filesystem it is always 4% full to start out with. That is how I arrived at that number.


Jim Hirschauer

http://www.aixexpert.com

 

[Mag0007]

HAHAHA! Duh!

Its a monday morning here!

 

[Mag0007]

Well,

I just added 10240 megs to a filesystem (according to lsvg)

but

df -kI shows only 4.5 extra gigs being added...

wierd!

thats a lot of overhead!

 

[RodKnowlton]

do

lsfs -q <filesystem>

I bet your nbpi is 8192, which would limit your filesystem to 128GB, no matter how large the containing logical volume.

To increase the nbpi, you'll have to create a new filesystem.



Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[Mag0007]

Hmm..

My nbpi is set to

(lv size: 267348352, fs size: 267348352, frag size: 4096, nbpi: 16384, compress: no, bf: true, ag: 64)

 

[hirschaj]

Are you sure you didn't add you 10GB in 512-byte blocks? If you did that you would have really been adding 5 GB and the 4% overhead would still hold true.


Jim Hirschauer

http://www.aixexpert.com

 

[Mag0007]

nope its all in 1024 bytes.

lsvg shows 10gigs being lost in the Total PPs section.

 

[RodKnowlton]

That was my first thought, hirschaj, until I saw that Mag00007 had said it was 10GB "according to lsvg".

Mag0007,

What command(s) did you use to increase the filesystem size?

Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[Mag0007]

i used chfs

 

[RodKnowlton]

with what arguments?


Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[Mag0007]

chfs -a size=+20971520 /filesystem

 

[RodKnowlton]

Could someone have been chewing up space on the filesystem while you were adding the space?

I just added a 128MB PP to a filesystem that was getting tight, and almost 97% of it showed up as added space.



Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+

 

[Mag0007]

Rod:
no, one one could be chewing up the space.

I also did a defrag on it too...still nothing :-(

BTW, this is a LARGE filesystem (135 gigs)....did you do your test on a large filesystem?

 

[ggauthier]

The overhead is not always 4%.

$ df -k /data1
Filesystem 1024-blocks Free %Used Iused %Iused Mounted on
/dev/data01 34603008 34329652 1% 17 1% /data1

The filesystem is comprised of 132 LPs @ 256 MB per.

frag size = 4096 ; NBPI = 16384 ; ag = 8


As for the other problem, if the lv size and fs size in lsfs match, and if you can account for all LPs in the volume group showing up in filesystems or jfslogs, then I wouldn't consider this to be a technical problem. It could be a match problem at the start.

-glenn