Re: 3 par recovery manager for Oracle (HP Product)
Date: Thu, 16 Jan 2014 00:39:13 -0200
Message-ID: <CAJ2dSGSMHf8J-Tf9VhTQHNgrREfwOiYEtbspN99XNd48n46f9Q_at_mail.gmail.com>
my understanding of this provisioning is the following: the SAN has a bunch of disks, let's assume they are all in a single pool, meaning that the LUNs will be split among all those disks. RAID level is unimportant for this, it's about space. So, let's say we have a small ideal SAN with 8 disks at 100G each. That means we have 800G available in the entire SAN. Now, most people like to have some free space on their LUNs to allow for growth, so for each 100G someone requests for a filesystem (or ASM disk) we can expect to have about 30% of that space free. Thin Provisioning doesn't actually allocate all the "free space" from the start (quiet like how autoextend works for oracle datafiles, only the LUN is the datafile). So you could have more than 800G "presented" to the hosts but not actually allocated. If you have 9 100G luns (you would have 900G presented, but since we estimate that roughly 30% of allocated space is not actually used, we could have roughly 1TB assigned before we ran out of actual space on the SAN). however, if the SAN runs out of space to allocate to the LUN it will stop adding it. But since ASM sees a 1TB ASM Disk it will assume the space is there and write it anyway. I don't know why or how ASM writes without getting a confirmation (or worse, if the SAN is sending a confirmation for something it has not actually written). This leads to corruption, the disks will go offline and the DG will be dismounted (incidentally, if you lose a ctl or access to system, sysaux,undo or all members of a redo log group instance will crash). This leaves the database in an inconsistent state almost always and the disks need to be recreated.
hth
Alan.-
On Wed, Jan 15, 2014 at 1:55 PM, Dba DBA <oracledbaquestions_at_gmail.com>wrote:
> So if I am using ASM. Would I see the 1 TB of data in my mpath file
> system?(we use redhat) So I can make a 1 TB ASM diskgroup, but behind
> the seens I would only get 200 gb? Then leave autoextend on and as I
> grow get allocated more space?
>
> There is an oracle white paper about thin provisioning with ASM. I am
> trying to understand this.
>
> The impression I got is that the SAN engineer sets this up at the LUN
> level and presents this to your server in the mpath file, but your
> really not getting that much space. Its in a pool that can be used by
> other servers, etc...
>
> One concern I had with this is the the performance hit from
> incrementally requesting more space from the SAN if I have a fast
> growing DB. The oracle white paper touched on this briefly by saying
> you can configure 3par with how much you request at a time. I also
> don't know if this can lead to a bottleneck if there are several
> servers requesting space from the same LUN at the same time.
>
> My SAN knowledge is rudimentary.
>
>
> On 1/14/14, Mark Bobak <Mark.Bobak_at_proquest.com> wrote:
> > Thin provisioning just means that not all the space that the storage
> array
> > has promised you, is actually reserved and allocated to you.
> >
> > If devices are thin provisioned, you could ask for 1TB of storage, and
> you'd
> > think, from the host's point of view, that you have 1TB of storage.
> But, if
> > you've only used 200GB, that's all the array has allocated to you.
> >
> > -Mark
> >
> > From: Dba DBA
> > <oracledbaquestions_at_gmail.com<mailto:oracledbaquestions_at_gmail.com>>
> > Reply-To:
> > "oracledbaquestions_at_gmail.com<mailto:oracledbaquestions_at_gmail.com>"
> > <oracledbaquestions_at_gmail.com<mailto:oracledbaquestions_at_gmail.com>>
> > Date: Tuesday, January 14, 2014 at 11:30 AM
> > To: ORACLE-L <oracle-l_at_freelists.org<mailto:oracle-l_at_freelists.org>>
> > Subject: Re: 3 par recovery manager for Oracle (HP Product)
> >
> > our SAs are talking about something called 'thin provisioning'. I have
> not
> > had a chance to dig into that.
> >
> >
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>
-- http://www.freelists.org/webpage/oracle-lReceived on Thu Jan 16 2014 - 03:39:13 CET