percentage of free space in the vxfs file system

[kirill.cherkashin]

Hi there,

Could you advise me at which level i should keep percentage of free space for vxfs?
According to veritas manual it should be not less than 10%.

"In general, VxFS works best if the percentage of free space in the file system does
not get below 10 percent. This is because file systems with 10 percent or more
free space have less fragmentation and better extent allocation." - from Veritas™ File System Administrator's Guide HP-UX 5.0

But the thing is that my FS are quite static. We have only limited number of database files on it. therefore fragmentation defenetely is not a issue.
Should I still maintain 10% of free space or could I increase the FS usage up to 99,99% ?

[Steven E. Protter · Accepted solution]

Shalom,

To quote our fearless leader, A. Clay Stephenson, the answer is, it depends.

If the data is relatively static it doesn't make a difference.

Even 99.99% usage would not be a problem. You'd be setting off monitor alarms at that level.

Example.

I had a system that was tight on /opt and /usr because it was stuffed full of software.

I operated it for a year at 97% /opt and 95% /usr because unless I patch or install software, there is no problems to deal with.

Full file systems are a bad idea, because if they are writable a modify attempt could spawn a file copy and then if the file system is critical, you risk a system stop.

I think for the sake of flexibility, maintaining a margin of error of 10% is a good idea.

SEP

[James R. Ferguson]

Hi:

Aside from the citation you made, I would certainly leave a 10% free space for unanticipated growth.

Another reason to leave the cushion of free extents is for times that you may want (or need) to uplift the VxFS filesystem layout version level. This requires free space, too.

Regards!

...JRF...

[kirill.cherkashin]

thanks for all answers.

Forgot to mention. files are constantly modified and updated. it's IBM Tivoli Storage Manager database, storage pool and logs files.

Their sizes and numbers are completely static . The growth controlled manually . So everything is pretty static for these FSs but not its content.

what does it mean "modify attempt could spawn a file copy"?

Could update of any of this files cause service degration? i don't speak about faults because half of FS's already have utilization 100%? ;-)

Kirill

[Bill Hassell]

Actually, the original restriction about 10% free came from HFS filesystems where the extra space was available only to root. And for HFS, approaching the 90% full level would cause long delays in allocating additional space such as adding files. But there was no effect at all on reading and writing where the writes were within the boundaries of existing files.

VxFS is similar -- when you push beyond 90%, it's like looking for a parking space in a lot that is 90% full. There's a lot of driving needed to find the right size space to park the truck.

But there is another reason to leave some space: Online JFS cannot expand a filesystem if there are no free extents in the filesystem. That can be a much bigger problem.

Now as to percentage, 90% is meaningless today when filesystems are dozens of GB in size. 10% of 2 TB is 200 GB, far more than needed to resize the filesystem. I would always leave 5 or 10 extents free (not a percentage) in a VxFS filesystem. As you mentioned, databases and other random access files usually get allocated one size and work within that size, thus creating a static filesystem.

[kirill.cherkashin]

All answers were quite useful and it answered on all aspects of my problem.