Thread: LVM vs Tablespaces

Hi,

I am curious what people think on this subject.  In the case that you have a database running on hardware which has two
separatedata volumes (lets call them data1 and data2), what is the "best" way for PostgreSQL to use those two volumes?
Sositting here I can think of two very simple ways of allowing PostgreSQL to use those two volumes: 

1) Tablespaces with simple partitions - This is simply create them as /data1 and /data2 then run "create tablespace" to
createan additional tablespace on the second data partition then move objects into it. 
2) LVM - Use LVM to create one single partition (which encompasses both volumes, for the purposes of this I am assuming
thesevolumes are already redundant behind hardware raid), then we have the default tablespace which sits on the larger
LVMvolume. 

So what do people think is the "best" way and why?  By "best", I dont have any preconditions in mind, some people may
considerblistering performance to be the number one concern and others may consider ease of maintenance to be the
numberone, either way both are valid interpretations of "best" and there might be different answers, hence I am
wonderingwhat people think is best and what makes it best? 

Thanks for your time.

Scott

--
Scott Neville
Software Developer, Bluestar Software
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Web site: www.bluestar-software.co.uk
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Email: scott.neville@bluestar-software.co.uk

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Scott Neville wrote:
> I am curious what people think on this subject.  In the case that you have a database running on
> hardware which has two separate data volumes (lets call them data1 and data2), what is the "best" way
> for PostgreSQL to use those two volumes?  So sitting here I can think of two very simple ways of
> allowing PostgreSQL to use those two volumes:
> 
> 1) Tablespaces with simple partitions - This is simply create them as /data1 and /data2 then run
> "create tablespace" to create an additional tablespace on the second data partition then move objects
> into it.
> 2) LVM - Use LVM to create one single partition (which encompasses both volumes, for the purposes of
> this I am assuming these volumes are already redundant behind hardware raid), then we have the default
> tablespace which sits on the larger LVM volume.
> 
> So what do people think is the "best" way and why?  By "best", I dont have any preconditions in mind,
> some people may consider blistering performance to be the number one concern and others may consider
> ease of maintenance to be the number one, either way both are valid interpretations of "best" and
> there might be different answers, hence I am wondering what people think is best and what makes it
> best?

With Version 1 you might end up with better I/O-performance because you'll use two
devices with two I/O queues, but I'm not sure of that.

When it comes to ease of maintenance, version 2 (striping) is much better, because you
don't have to manage tablespaces, which can be a pain for backup/restore.
You also don't have to think about data placement.

We have a setup like version 2 and are pretty happy with it.

Yours,
Laurenz Albe