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RE: Sizing - RAC, storage subsystem EMC

From: Cary Millsap <>
Date: Thu, 22 May 2003 08:42:16 -0800
Message-ID: <>

Oh man, .One parity disk for 10-20 disks means that if *any* single disk in the group fails (which will happen five times more frequently in a 20-drive group than in a 4-drive group), then for the duration of the partial outage every single read from the failed disk is going to engage all 10-20 disks in the group. And the resynchronization of the new disk, once it's plugged in, is going to require the *full disk scan of all 10-20 devices*. I wouldn't want to be anywhere nearby when *that* happened.  

Cary Millsap
Hotsos Enterprises, Ltd.

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-----Original Message-----
Sent: Wednesday, May 21, 2003 12:17 PM
To: Multiple recipients of list ORACLE-L  

Depends on how much cache you got and how many DB servers is the SAN serving. Once your cache

is saturated by reads and writes, RAID 5 is going to hurt you.

-----Original Message-----
Sent: Wednesday, May 21, 2003 8:55 AM
To: Multiple recipients of list ORACLE-L

With EMC, or any other SAN, you do not write to the disks. You write into a cache memory on the controller and the controller then writes the data to the disks at his own time. If you have big enough write cache on the controller the raid-5 write speed does not concern you.  

Raid-5 might be a little slow but it save almost 1/2 the disk space needed to ensure the correctness of the data since it can use one parity disk for 10-20 disks.  

Yechiel Adar

To: Multiple recipients <> of list ORACLE-L

Sent: Tuesday, May 20, 2003 9:06 AM  

Hi all, hope you can give some input ideas.  

I am in the process of designing a system for a client of ours for a proposal  

The sizing information I have been given is as follows.  

58.1 million tickets/day at 351 bytes per record. The record was complete populated (all columns filled to max) in a table and then analyzed. Average row size 351 bytes.

=~ 19 GB/day. Raw data. Plus overhead (indexes, temp space, rollback, some other data etc) here and there I have requested 5 TB.  

We need to keep records for a month. Table design I am looking at is a date partition with a second level hash partition. This is so that I can move data in the oldest week/table space off line and write them to optical storage for possible retrieval at a later date (requirement).  

Of course this will be on locally managed table spaces with auto storage management for segments.  


The database will be a Oracle RAC on Sun cluster 3 build on 2 x Sun StarFire V880, 4 CPU's, 4 GB RAM each,

Connected to an EMC SAN via Fiber Channel  

I do not have more information about the EMC array at the moment. Hitachi has been mentioned. (excuse the spelling)  

Question I have.  

I have been asked how many writes the Database will be doing to the SAN per second.

I have determined that I should expect about 2000 tickets/second.

The table in question will have 2 indexes.  

Now following rough guessing I said I should expect at least 16 000 writes/second  

This was done by say/assuming  

2 writes for the redo log files (2 members)

2 writes for the control files (2 control files)

2 writes to index blocks

1 write to undo table space block

1 write to table block for data

total 8 blocks written to per ticket.  

Now I know the above is a real rough. And probably very wrong, if someone can shed some more light on it and give me a more accurate method/guess I would appreciate it.  

Another question.

The hardware SAN engineers are telling me they want to configure the SAN in a RAID 5 configuration. I have requested Raid 0 + 1. They say this is going to be to expensive and the new technology allows them to give me the performance I want using RAID 5.  

I would prefer to err on the side of caution and follow Oracle industry wide recommendation and follow the SAME methodology.




George Leonard  

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You Are Committed to Educate Yourself to the Total Risk In Any Activity!

Once Informed & Totally Aware of the Risk, Every Fool Has the Right to Kill or Injure Themselves as They See Fit!  

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Author: Cary Millsap

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Received on Thu May 22 2003 - 11:42:16 CDT

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