LVM Performance vs. # of disks

[Reston Tech Support]

There's a debate going around among the SAs in our group. We have some V-Class servers hooked up to EMC frames, and the question concerns the max # of disks in a volume group to maximize performance.
One guy says his instructor in class said there shouldn't be more than 4 or 5 disks in a volume group or you will suffer performance issues. When I called HP, the CE said the amount of disks in the volume group does not impact its performance and you can have as many as you want.

Does anyone else have an opinion on this?

TIA
FD

[Stefan Farrelly · Accepted solution]

Ive never ever heard of anyone staiting before that over 4/5 disks in a VG slows down performance ! Im astounded someone would make a claim which in my opinion is not proveable. In fact the more disks in a VG - so that you can stripe lvols across them - increases IO performance, not decreases it !

[Wim Rombauts]

Stefan is right.

The better you can spread your data over multiple physical disks, the better your performance.

[harry d brown jr]

I have to side with HP on this one. Creating too many volume groups and too many logical volumes is a management nightmare and should be avoided.

Was it an EMC instructor that said that VG's should only have 4 or 5 disks in it?

[harry d brown jr]

Imagine this: You have a database or some other data-pig that is one terabyte. You have an array of 18gb disks. Using the 4 or 5 disks per VG would force you to create 12 VG's. Was the instructor having a bad acid day?

[Reston Tech Support]

Well Harry, that indeed is the issue. We do have systems with terabytes of space on them. Some of our Oracle (project) volume groups are well in the hundreds of gigabytes. I (and others) like to engineer it so that we have one vg per project, with about 8 lv's per vg. Managment wise, it works out nicely. But when we spread a project among 4 or 5 vgs because of perceived performance gains, it does make managing it somewhat more difficult, which is what raised the issue to begin with.

[Thierry Poels_1]

hi,

maybe there was some confusion: more than 4-5 disks in one SCSI-chain might decrease performance because the SCSI-chain might be overloaded.

regards,
Thierry.

[Hrvoje Dubravica]

Hi,
I also have HP-EMC and HP-XP env. and many
vg with various number of disks in volume groups. I havent seen # of disks per vg influence on performance. Most importen thing is on storage side. You must take disks from
diffrent controler units (XP), disk directors (EMC) to have better perfomance, and use more
then on FC adapter on host side.
:-)

[harry d brown jr]

Reston, stick to your guns, because you are doing the right thing!!!!

[Stefan Farrelly]

After some more thought I came up with the same answer as Thierry has already replied - someone has mixed 4/5 disks per VG with the old performance constraint of 4/5 disks per controller (FWD SCSI type) !