Re: To LVM or not to LVM?

From: Rich J <>
Date: Wed, 08 May 2019 15:09:18 -0500
Message-ID: <>

On 2019/05/08 08:50, Stefan Koehler wrote:

> Hello Rich,
> VMFS or RDM is important because the number of LUNs per VMware host is limited ( ) and also important because of the disk device queue.

>> If that's the case, then I can see potential for LVM in creating small(er) LUNs and grouping the corresponding PVs into a VG to spread the load with a striped LV.

> I know IBM's XIV as well but my point is a different one as it is related to the host site only. You got only one disk device queue if you just got one LUN (e.g. like you mentioned in the other mail "get a 500GB virtual disk and I create a single partition on it, add XFS, and create a mountpoint for it") for your database. This is not a big deal if your database is not I/O intensive but as soon as you got high I/O load you will see effects of increasing I/O latency because of increasing device queue ( e.g. storage wait time vs. host wait time: ) up to a point of a full disk device queue ( e.g. wait event "db file async I/O submit": ).
> These disk device queue problems can be handled with striped LVs :)

Interesting! Queuing then would seem to depend in part on the SAN setup. If I only get a single RAID group exposed to OL7 via VMWare, much of this is moot.

Lots of things to consider, but this would definitely be a large point in favor of using LVM. I get it now. Having been on the XIV for so long had blinded

Thanks much!


Received on Wed May 08 2019 - 22:09:18 CEST

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