Performance issues with LVM file systems over 90 %

[Rai Fedorowicz_1]

I'm running hp-ux 11.11 on an N class system. I have 8 LVM file systems that are now over 90% full, one is at 97%. These are used for Oracle database 11.5.9 and the DBA creates more tables to increase the file system size. Are there any performance issues when the file systems go over 90%.

[A. Clay Stephenson]

There is no such thing as an LVM filesystem. An LVM LVOL can be the container for a filesystem but the type of filesystem will be vxfs or hfs. Because vxfs filesystems (I assume vxfs filesystems are what you are using) are extent-based, the largest possible chunks are assembled regardless of the underlying blocksize. When filesystems get very full there is some concern about fragmentation but in the vast majority of cases defragging the filesystem has almost no measurable performance impact. Moreover, because Oracler files are normally preallocated, fragmentation is not an issue. In your case, my main concern would not be performance but rather that the DBA will need additional space in the middle of the night or weekend. For that reason, I would allocate some additional space. In my case, my OV/O alarms go off when Oracle filesystems hit 93% but that always leaves me enough headroom to fix things on a Monday morning.

[Steven E. Protter]

Shalom Rai,

As a filesytem gets full, its common to have these issues. I generally get uncomfortable running fileystems with dynamic data(re oracle) with a filesystem that is more than 80% full.

It kind of depends how the filesystem is used though. You might, if you have OnlineJFS defrag on the filesystem, though its better to expand it.

SEP

[Rai Fedorowicz_1]

Sorry for the confusion, but yes it is a Vxfs file system with LVM lvols. The LUNs are on a VA7400 and I can not increase the lvol sizes even though I am running Online JFS because they are using all of the LUN size. It looks like I need to redo the VA7400 this weekend and then redo my VG and lvols. I thought I had heard about performance issues but from your answers it looks like it isn't an issue.
Thanks for your information.

[Dave Olker]

Hello Rai,

My colleague Mark Ray has written extensively on this subject, and given lectures on it at forums like HP World. His technical paper on JFS (VxFS) Performance is an excellent reference for any VxFS filesystem performance issue. You can find the latest version

http://docs.hp.com/en/5576/JFS_Tuning.pdf

While he may not talk specifically about how full to keep filesystems, he does discuss the issue of fragmentation, which becomes increasingly worse and harder to work around as filesystems get fuller.

Hope this helps,

Dave

[Trevor Roddam_1]

Rai.

I concur with all of the above; however, in regards to having a VA with all the disk space fully allocated.....

The VA array is very similar to the 12H in that if it is over 75% allocated and that space is used (IE at 90%) then the VA will slow down significantly as the amount of changed blocks increases.

This is due to the "AutoRAID" nature of the VA. If you are having performance issues I would look at the VA and get some stats from it. The "Write Working Set" is probably very small and the VA will move to writing to RAID 5 not RAID 1+0. It can halve the performance from normal and it is a very quick slide into very low performance once this becomes the issue.

The performance drop on VA's when under this stress has been a known issue for some time and little understood.
Basicly, get more disk. Be carefull not to buy just one large disk as the virtual sparing may actually reduce the usable space.

Please post some more detail in regards to the VA if this is you're issue. I have some exp with them and it can be fairly simple to diagnose, not always easy to fix.

[Paul Bardeskar]

Hi Rai,

You are running Oracle Database with a file system which is 97 % full, Though it will not lead to any performance issues. But you will certainly have problems once the file system grows to 100 % or any of your Oracle Table Space grows to 100%.

Suggestion is to cleanup or your File System or increase the File System.

Cheers,
Paul

[Rai Fedorowicz_1]

Thanks for all the good comments. When the company purchased the VA, Business Copy was also purchased. I had heard that there were issue with running in AutoRaid with an Oracle database so the VA was set up 0 + 1. We have not used the Business Copy because it really didn't give us what we were looking for. The plan now is to remove BC to give us back disk space.
We have purchased all new equipment, rp8420 and EVA5000 to go live end of Jan and hoping to last until then, but it looks like I will have to make changes to current equipment.
Again, thanks for all the good information.

[Ted Buis]

Just for the record, if it was an hfs file system at 97% full, you would have performance degredation. The vxfs is much better than hfs in this regard, but unless the system is static, you are at some risk of not having the room you need.

[Shameer.V.A]

Hi Rai,
Please rate the suggestions with appropriate points. This will increase the response to your queries. YOu have not rated any single answer.

shameer