Re: ASM IO distribution on a SAN

  • From: "Alex Gorbachev" <ag@xxxxxxxxxxxx>
  • To: ryan_gaffuri@xxxxxxxxxxx
  • Date: Thu, 13 Sep 2007 16:25:55 -0400

No. ASM will play the role of LVM and with LVM you setup LVs (Logical
Volumes) not LUNs.

LUN is what coming from your SAN - it's like SCSI disk for your OS
(/dev/sd... or /dev/emcpower... if you use multipathing and etc.).

When you configure LVM, you first create PV (physical volume) on each
LUN from your SAN. Then you group PVs into VGs (volume groups). In
each VG you can create one or more LVs (logical volume). After that
you usually format your LV with a filesyste or you can use it as raw
device. Theoretically, it's possible to setup ASM on top of it (and
I've done it on practice - worked fine) but you don't really want to
do that.

With ASM you just create diskgroup from a set of disks/LUNs. If you
want to map ASM and LVM terminology:
- LUN formated as LVM PV = ASM disk (formated implicitly)
- LVM VG = ASM DG in concept but DG is much more than that - it's VG
with LV with special kind of filesystem.

There is no notion of LV in ASM. You can think that it's automatically
creates one big LV on DG and formats it with special filesystem. On
the other hand, conceptually, LV is also close to a file inside ASM
diskgroup.

I hope these analogies help.

On 9/13/07, ryan_gaffuri@xxxxxxxxxxx <ryan_gaffuri@xxxxxxxxxxx> wrote:
>
> so I still need to set up the luns with an LVM? and then put one disk group
> on each LUN.
>
> I think I got it.
>
> -------------- Original message --------------
> From: "Matthew Zito" <mzito@xxxxxxxxxxx>
>
>
>
> It is unlikely your storage array has the capability to present a multi-TB
> lun, or that from an administrative perspective you would want such a thing.
>  ASM would be a fine way to evenly distribute IO across a series of
> reasonably sized LUNs.  I think Paul's point was to not count on the
> striping from a performance perspective, simply an administrative ones.
>
> Matt
>
> --
> Matthew Zito
> Chief Scientist
> GridApp Systems
> P: 646-452-4090
> mzito@xxxxxxxxxxx
> http://www.gridapp.com
>
>
>
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx on behalf of ryan_gaffuri@xxxxxxxxxxx
> Sent: Thu 9/13/2007 12:58 PM
> To: paul.baumgartel@xxxxxxxxxxxxxxxxx;
> oracle-l@xxxxxxxxxxxxx
> Cc: Baumgartel, Paul
> Subject: RE: ASM IO distribution on a SAN
>
> So I don't need to ask the SAN admins to set up a series of LUNs? They can
> just make me one big mount point for my datafiles and it will be evenly
> distributed?
>
> We may be talking 5 TBs/day of data we are inserting at full deployment plus
> 4 million queries.
>
>
>


-- 
Alex Gorbachev, Oracle DBA Brewer, The Pythian Group
http://www.pythian.com/blogs/author/alex http://www.oracloid.com
BAAG party - www.BattleAgainstAnyGuess.com
--
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