Re: Which oracle server ?

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Mon, 13 Dec 2004 18:29:53 +1100
Message-ID: <41bd44eb$0$5112$afc38c87@news.optusnet.com.au>

DA Morgan wrote:
> Howard J. Rogers wrote:
>

>>> You don't want to use raid 5.  
>>
>>
>> He might do.
>>
>> HJR

>
>
> Source:
> http://download-west.oracle.com/docs/cd/B14117_01/server.101/b10752/instance_tune.htm#23421
>
> Quote:
> "Move the redo logs to faster disks or a faster I/O subsystem (for
> example, switch from RAID 5 to RAID 1)."

He has three hard disks, Daniel. Care to tell me how to implement RAID 1 for his redo logs with that lot? Whilst not, of course, putting all his datafile I/O onto a single hard disk.

> Source:
> http://download-west.oracle.com/docs/cd/B14117_01/server.101/b10752/iodesign.htm#26022
>
> Quote:
> "Avoiding the use of RAID 5 for redo logs."

"Avoid the use of RAID 5" and "The use of RAID 5 is prohibited" are two statements that mean entirely different things. Work it out.

> Source:
> http://download-west.oracle.com/docs/html/B13831_01/tuning.htm#sthref531
> Quote:
> "Striping data across a number of disks is one example of a redundant
> array of inexpensive disks (RAID). There are several different types of
> RAID, also referred to as RAID levels, ranging from high performance to
> high reliability. The three most common RAID levels in Oracle Database
> installations are RAID-0, RAID-1, and RAID-5. Descriptions of each RAID
> level follow Table 7-2, which shows each level's read and write penalties.
>
> RAID Level Read Penalty Write Penalty
> 0 (Disk Striping) 1:1 1:1
> 1 (Disk Mirroring) 1:1 2:1
> 0 + 1 1:1 2:1
> 5 (Distributed Data Gathering) 1:1 4:1"
> .. and ..
> "The write penalty of 4:1 results from 2 reads and 2 writes during
> parity calculation."
>
> Source:
> http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96533/iodesign.htm#22610
>
> Quote:
> "RAID 0+1: Striping and Mirroring
> This level combines the technologies of RAID 0 and RAID 1. It is widely
> used because it provides good reliability and better read and write
> performance than RAID 1."
> and
> "RAID 5 striping is similar to striping in RAID 0 ... while write
> performance can suffer. This configuration might not be ideal for
> write-intensive applications."

Oh look. The word "might" makes an appearance. Gosh.

And as for RAID 0+1... care to tell me how he sets that up with three hard disks?

> You are, of course, correct as always and I have obviously
> misunderstood. Thank you, in advance, for correcting both me and Oracle.

You know, you really do make yourself look more and more foolish as this silliness of yours continues.

I said he *may* do. He has more problems than RAID5, and I would suggest that it *might* be the case that he would be better off fixing them than worrying about his RAID levels. "May" and "might" do not a contradiction of Oracle Corporation make.

Do you know whether the OP is a Data Warehouse, or an OLTP environment? I may have overlooked that nugget of critical information in the original post (clue: I didn't). If his database is read-mostly, what the hell does a bit of write-penalty matter? Compared with, say, the lack of support for his planned O/S??

There is more to consider here, in other words, than just trotting out broadside advice about RAID 5 (which I must say I rather expected you to do, sooner or later).

HJR Received on Mon Dec 13 2004 - 01:29:53 CST