Re: ASM LUN sizes and number of disks
Date: Mon, 10 Nov 2008 09:19:02 +0000 (GMT)
I am still confused (although i do agree with ideas of Greg) Is there a paper which describes whats the ideal combination of disks and sik sizes for ASM.
I am using external redundancy should i still be worried about having only 2 disks ?
I am planning to add 2 2000Gb disks and then simulatenously drop the 6 50Gb disks so rebalance is a single operation
- On Sat, 8/11/08, Greg Rahn <greg_at_structureddata.org> wrote:
> From: Greg Rahn <greg_at_structureddata.org>
> Subject: Re: ASM LUN sizes and number of disks
> To: finn.oracledba_at_gmail.com
> Cc: hrishys_at_yahoo.co.uk, oracle-l_at_freelists.org
> Date: Saturday, 8 November, 2008, 4:36 AM
> On Fri, Nov 7, 2008 at 6:55 PM, Finn Jorgensen
> <finn.oracledba_at_gmail.com> wrote:
> > Because of the way ASM distributes data evenly across
> all disks in a
> > diskgroup, adding 200GB disks to an existing diskgroup
> comprising of 50GB
> > disks means you will never be able to use more than
> 50GB of those 200GB
> > disks.
> I agree with this...
> > You will have to add those disks to a separate
> diskgroup and then start
> > moving data over, which means downtime.
> but could you not add(2x200)/rebalance,
> drop(6x50GB)/rebalance to get
> all the data onto the 2x200GB?
> this would alleviate downtime but...
> I would never put my whole database only on 2 spindles
> anyway. If I
> recall correctly, if there is not room to mirror ASM
> extents from the
> failed drive, the diskgroup will dismount to protect from
> failure. This means in a two disk ASM group, losing one
> disk will
> result in a down database. There there is also a special
> case with 3
> disks, as each is in their own failgroup and I believe the
> space (for files) for 3 disks is the same as 2 disks (or
> similar). So basically the minimum recommended disks is
> four. It
> comes back to disk space is cheap...
> Greg Rahn