RE: SAN configuration for Banner

Hi  

I *think* but I may have entirely misread the comment that point 4 is just wrong. It sounds like you only have one raid 5 set (which is shared between 2 machines). If this is the case then the clustering has no effect on the fault tolerance/performance of the raid 5 set. Or am i just on crack here?  

Point 5. writing to the datafiles *may* be acceptable on a raid5 set (it just depends what the volume of write activity is - does anyone have any idea what the IO requirements will be? if so do the calculations), writing to redo/archive almost certainly won't be. I'd hold out for Raid 1 for the logs and maybe compromise on Raid 5 for the data.  

as for the last point, I'd also like to see the justification for raid5 is 3 times more likely to suffer dataloss. I'm afraid that a) I don't think I believe it and b) you've got the logs anyway :( OK just a) really.  

corrections and clarifications welcome.  

You may also wish to look at James Morle's SANE SAN paper at www.oaktable.net it would appear to be pertinent (and he does know whereof which he speaks)  

Niall

-----Original Message-----
Sam Bootsma
Sent: 19 November 2003 15:55
To: Multiple recipients of list ORACLE-L

Hi List,  

We are approaching the cusp of a decision on how to store Oracle data files on our SAN. We don't have the SAN yet, but it is due to arrive any week (if not any day).  

I passed Cary's "Is RAID 5 Really a Bargain?" paper to our Sys Admin, which he read and succinctly summarized for the Technical Manager here. I have also read through a couple of papers referenced in the BAARF site. The Sys Admin comments were:  

Dell would like to know what RAID mode we want configured on the SAN for the B80 and 6C4 computers. Sam has told me that, in the Oracle community, mirroring (RAID1) is preferred over RAID 5 for various reasons (RAID5 is: more costly for write-intensive applications, 3 times more likely to incur data loss, suffers from massive performance degradation during partial outages). RAID1 will be more costly per unit of usable storage. Mirroring seems to be the best choice. Let me know what you think.  

Here is the Manager's response:  

Any suggestions on how I can counter points 4 and 5 - and the last point before his "Thanks" line? Currently we have two B80's (AIX 4.3.3) set up in a HA configuration. They share an external disk array. So if a hardware component in the primary box fails, then it will automatically failover to the secondary box (and at the same time, the secondary box takes control of the external disk array). I think the clustering term in point (4) is referring to this setup.  

Thanks for any suggestions.  

Sam.    

Sent: November 18, 2003 5:08 PM  

All the points are valid...however..my thought processes were as follows:  

1. The System & Core Application disks are resident on the disks within the CPU and Mirrorred (Everyone OK with that I think)
2. The Databases are Resident on the SAN
3. The SAN disks are RAID 5 as the provide more usable space for the cost as compared to mirrorring
4. As the IBM Systems (B80's & 6C4's) are clusterd thus effectivley Mirrors the RAID 5 Arrays mitigating the issues Sam raises re preformance degradation (which will only ever arise in the event of a failed disk/automated rebuild which is usually configurable to address performance degradation)
5. Write to Disk/Commit to Database should be a background process
   (although I recognise this is a transaction/write intensive based
   system)

This is a standard model that all servers are being deployed with and unless there are any specific technical reasons why this will not work it is the way I would like to see the systems implemented. Remeber, with the SAN...Reconfiguration of Disks is not a large issue anymore if required in the future.  

Although not an AIX/Oracle guy...I disagree with the statement that RAID5 is 3 times more susceptable to incur Data Loss. RAID 5 is a proven technology  

Thanks..... Andrew  

-----Original Message-----
Sent: Tue 18/11/2003 2:56 PM
To: Andrew Riem
 Subject: SAN configuration for Banner  

Dell would like to know what RAID mode we want configured on the SAN for the B80 and 6C4 computers. Sam has told me that, in the Oracle community, mirroring (RAID1) is preferred over RAID 5 for various reasons (RAID5 is: more costly for write-intensive applications, 3 times more likely to incur data loss, suffers from massive performance degradation during partial outages). RAID1 will be more costly per unit of usable storage. Mirroring seems to be the best choice. Let me know what you think.  

Carl

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Author: Niall Litchfield
  INET: niall.litchfield_at_dial.pipex.com

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