Re: asm on san

From: DA Morgan <>
Date: Fri, 12 Dec 2008 12:07:24 -0800
Message-ID: <>

joel garry wrote:
> On Dec 11, 6:32 am, Mladen Gogala <> wrote:

>> helter skelter wrote:
>>> Hi,
>>> I'm preparing to test some configurations on san storage array. I would
>>> like to find out what will be better in my environment: raid1+0 or
>>> raid5. Other thing is what size of segment size should be configured on
>>> storage array. For example, I've got 5 disks in RAID5, so if ASM default
>>> stripe size for datafiles is 1MB, so segment size on strage shouls be
>>> 256KB to hit all drives, am I right?
>>> What tools are You recommend to do tests like this: sequentail/sequence
>>> reads etc?  thanks
>>> oracle 10gr2, rhel5
>> RAID 5 is not good for databases, period. Not for data files, especially not
>> for the log files, you can only use RAID 5 partition for log_archive_dest_25
>> If your boss told you to evaluate RAID 5, it is very likely that he wants to
>> save some money in the wrong place and will buy you RAID 5, no matter what
>> your findings are. Moan Isnogood has a great site at
>> The abbreviation "BAARF" stands for "Battle Against Any Raid Five". Your
>> company is probably doomed and will not make it through the recession. Have
>> a nice day.
>> --http://

> While I agree with you and Dan, having an interesting member number
> bitwise on baarf and general agreement on the principles, I have to
> admit that it works for my employer, who not only is not doomed but
> keeps me busy with expansion projects. Business needs uber alles and
> all that. The only time it is a problem is when it is operating in
> degraded mode or some rare thing overwhelms the buffering. The more
> usual case is akin to a mostly empty municiple bus, plenty of room for
> quite a bit more riders. I'd like to take the thanks for that, but
> really it's just a reasonable configuration for what it does (ERP/MRP
> OLTP, mostly). If I had to choose between Itanium hp-ux RAID-5 and
> Itanium Windows RAID-10, I wouldn't pick the Windows.
> jg
> --
> is bogus.
> Big packet must get through!

It is more than just when it is in degraded mode. RAID5 has substantial negative impacts on performance all of the time the system is not idle.

James Morle, at UKOUG, pointed out that a similar issue exists with the new Solid State drives too making them problematic for small writes.

If you shackle a system with RAID5 today, and later need the horsepower, you will find it almost impossible, from a practical standpoint, to get off RAID5. Better to say NO! now than later.

If they can't afford the disk ... the data isn't that important.

This is not to say backups couldn't be sitting on RAID5. But operational datafiles? redo log files? No way.

Daniel A. Morgan
Oracle Ace Director & Instructor
University of Washington (replace x with u to respond)
Puget Sound Oracle Users Group
Received on Fri Dec 12 2008 - 14:07:24 CST

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