topic Re: slow disk performance in Operating System - HP-UX

slow disk performance

John Oberlander — Thu, 17 Mar 2005 12:01:13 GMT

Im running HP-UX11i v1, on a HP9000 10cpu, 18G mem, and a Storageworks EVA / secure path A.3.0E.00F.00F. We are running Universe database for collections with alot of users and heavy read/writes. I just started at this company and kinda of a newbie when it comes to HP admin. The question i have is what is the normal percentage of free disk space you should have on a file system. If the logical volume is 90some% full, won't this hinder performance expecially for writes cause the data becomes more fragmented, and takes a longer time to find a place for consecutive writes? I've always followed 20% free in the linux ext2/3 world. Thanks in advance.

Re: slow disk performance

RAC_1 — Thu, 17 Mar 2005 12:24:37 GMT

I tend to keep about 10-15 % free. I also regularly do defrags. But most of the time it is not required. With VxFS file system, the space allocation is extend based. In order to get good performance, I tend to strip the data over available disks.

you should dir and extend fragmentation first before doing anything.

fsadm -E and -D options.

Re: slow disk performance

John Oberlander — Thu, 17 Mar 2005 12:28:20 GMT

I was told that our EVA is striped very well, it just seems like we cant touch the performance that we could get. Most of our LV's have 10-20% so it seems were fine there. All of our issues come down to diskIO and im just trying to eliminate some of the possibilities. Thanks for the info.

John

Re: slow disk performance

Ted Buis — Fri, 18 Mar 2005 18:24:42 GMT

I have always understood that you take a performance hit with file systems that are close to full. How many systems are attached to the EVA? You may be able to increase the queue depth (default is 8 in HP-UX, max 256) to take greater advantage of the EVA.