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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Re Raid 5+
Hello Tim
You wrote:
> There is the problem of synchronization and the impact of that synchronization on other simultaneous requests. Since all
> 11-12 devices are servicing one request at a time, who gets served first?
The answer is of course: The blond with the big bosom.
Seriously: (and this is also a reply to Jared as well) The mail I answered to started with:
> I cannot fathom Raid 5 being faster than Raid 1 for writes.
Well in sequential writes like redo log, copy redo log to archive log and many other cases raid 5 will be faster.
Yechiel Adar
Mehish
...using a similar rationale, nine women could produce a baby in a month...
There is the problem of synchronization and the impact of that synchronization on other simultaneous requests. Since all 11-12 devices are servicing one request at a time, who gets served first? Sure, there are optimizations to ensure that "whoever is closest" will get served first, but it still implies single-threading at the slowest part of the subsytem. While the stated rationale surely sounds good for one user, what is the impact of such an arrangement for a hundred concurrent users?
Hello Ian
I heard a lecture on raid 5 disks a few weeks ago. The rational behind read 5 being faster then raid 0+1 is this: You have 12 disks. In raid 0+1 you use striping across 6 volumes. In raid 5 you strip across 11 disks, so you get almost double the work without returning and moving the r/w head on the same disk.
Yechiel Adar
Mehish
I cannot fathom Raid 5 being faster than Raid 1 tor writes. The real question is, is it fast enough for your users. We happen to have a 650 terabyte database here. Even using Raid 5 disk storage would be prohibitedly expensive. So we use a home-built hierarchal storage system and store much of the data on Redwood tape drives. Users know that requesting data from the Redwood drives will take some time. But they were told to expect that. (The database is Objectivity not Oracle, and I have nothing to do with it). The online data as opposed to the near-line data is stored in Raid 5 arrays.
What I don't know is what percentage of Oracle databases can run fine on Raid 5 vs. Raid 1. It would not surprise me if the answer was well over 50%
Ian MacGregor
Stanford Linear Accelerator Center
ian_at_SLAC.Stanford.edu
-----Original Message-----
From: John Hallas [mailto:john.hallas_at_hcresources.co.uk]
Sent: Thursday, October 31, 2002 12:34 AM
To: Multiple recipients of list ORACLE-L
Subject: Re Raid 5+
Jared,
We are certainly going to be performing extensive testing to ensure performance of our applications under Raid5+ is acceptable.
That means it is as good if not better than that experienced under Raid1
As I see it Oracle gain no benefit for stating that Raid5 should be used if they did not believe that to be the case. If there was any doubt it would be easier fro them to leave things as they were
John
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Yechiel Adar INET: adar76_at_inter.net.il Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Mon Nov 04 2002 - 02:13:21 CST
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