Effect (slow down?) using LVM on LUN
 

Good afternoon! I'm looking for pointers to information or opinions on using LVM to manage space presented from a SAN. I'm mainly curious as to the effects using LVM can have on access speeds, if there is any. There are some similar threads on LVM & SAN space, I know LVM will manage the space just fine. However I've not seen anything aiming at answering impact on speed.

In this particular case, we're using RHEL 5.4, HP DM Multipath to handle the fiber connections, and QLogic HBAs (not sure if that makes any difference).

I'd like to use LVM due to the ease of adding space later if needed. Does LVM add enough overhead that I should reconsider?

Thanks!
Kara

No.

LVM adds no significant performance impact. It's main overhead is additional disk space used for its structures but even that isn't any worse than say using software RAID or a filesystem (though of course you'll put filesystems on top of the LVs and use a little more space).

The benefits to using it outweigh not using in my mind.

I've used LVM quite extensively on HP-UX for more than 10 years and on Linux both for internal storage, internal RAID storage and external SAN attached storage without any noticeable performance issues for the last 4-5 years.

With the important caveat that I haven't actually measured performance differences, I can also say that LVM on top of DM Multipath on top of SAN LUNs delivers very acceptable performance.

And I'd reiterate the point above: what good, functional alternative do you have? (If you have one, I'd like to know, actually.)

Great! That was the answer I was hoping for. Thanks for both of your input. I hadn't noticed any issues using LVM for local storage but wasn't sure of it in other situations.

anomie,
I'm not aware of an alternative to LVM.

Actually Veritas (excuse me - now Symantec) Storage Foundation is an "alternative" but it is FO$$ (Financial Outlay Static Software :D) as opposed to FOSS. Its Volume Manager offers quite a bit of flexibility especially in cluster environments but although I've used it on both HP-UX and Solaris I've not used it on Linux. Is has both the volume manager and the Veritas Journaled Filesystem which allows for some fairly impressive scaling and is more mature than ext4 and some of the newer filesystems offered in Linux.