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RE: Sizing - RAC, storage subsystem EMC

From: Michael Boligan <>
Date: Thu, 22 May 2003 10:27:10 -0800
Message-ID: <>

Yes, RAID 5 would be ugly. Doesn't EMC use RAID-s though, which stores a copy of the parity on all drives. It was a while ago that I used EMC, so things may have changed, or more likely, my memory is warped....

Can anyone confirm this (no, not that my memory is warped, that has been confirmed plenty of times).

Mike Boligan

                      "Cary Millsap"                                                                                               
                      <cary.millsap_at_hot        To:       Multiple recipients of list ORACLE-L <>               
            >                 cc:                                                                                 
                      Sent by:                 Subject:  RE: Sizing - RAC, storage subsystem EMC                                   
                      05/22/2003 12:42                                                                                             
                      Please respond to                                                                                            

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.

Upcoming events:
- Hotsos Clinic 101 in Reykjavik, Ottawa, Dallas, Washington, Denver, Sydney

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-----
      From: Yechiel Adar []
      Sent: Wednesday, May 21, 2003 8:55 AM
      To: Multiple recipients of list ORACLE-L
      Subject: Re: Sizing - RAC, storage subsystem EMC
      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
       ----- Original Message -----
       To: Multiple recipients of list ORACLE-L
       Sent: Tuesday, May 20, 2003 9:06 AM
       Subject: Sizing - RAC, storage subsystem EMC

       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

       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

       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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Author: Michael Boligan

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Received on Thu May 22 2003 - 13:27:10 CDT

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