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Re: RAID5+

From: Yechiel Adar <adar76_at_inter.net.il>
Date: Wed, 30 Oct 2002 08:44:20 -0800
Message-ID: <F001.004F78EF.20021030084420@fatcity.com>


Not a silly analogy - a very good one.

Yechiel Adar
Mehish
----- Original Message -----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Sent: Wednesday, October 30, 2002 3:29 AM

> As with any "cached" I/O subsystem technology (i.e. RAID-S, NetApps, etc),
> please visualize a water tank. The water tank represents the cache, the
> drain from the tank represents I/O throughput rates from the cache to the
> hard-drives, and the faucet filling the tank represents the I/O volumes
from
> the server to the I/O subsystem. The faucet filling the water tank is on
a
> valve, so that when the tank is full, it does not overflow. Let's say
that
> the water tank holds 100 gallons (about 400 liters???). The faucet
filling
> the water tank can vary its rate, anywhere from 1 gal/min to 30 gals/min.
> The drain from the water tank operates at 5 gals/min and can not be
blocked
> or closed.
>
> Got that pictured in your mind? Now for some scenarios...
>
> 1) What happens when the faucet is filling the water tank 24x7 at a
rate
> of 1 gallons/minute? No problem -- the tank never fills, so the flow into
> it is never impeded...
>
> 2) What happens when the faucet is filling the water tank 24x7 at a
rate
> of 5 gallons/minute? Still no problem -- the tank never fills, so the
flow
> into it is never impeded...
>
> 3) What happens when the faucet is filling the water tank 24x7 at a
rate
> of 6 gallons/minute? Uh oh. In less than two hours, the water tank will
> fill, causing the flow of water to be limited to the output rate of 5
> gals/min. Too bad, because we really need to move 360 gallons/hour, or
8640
> gallons/day, through this system...
>
> 4) What happens when the faucet is filling the water tank for an hour
at
> 10 gallons/minute for 15 minutes, then at 1 gal/min for the next 45
minutes?
> Not a problem -- the capacity of the tank was able to hold the excess
input
> rate during the first 15 minutes, and whatever accumuated was drained off
> before the next "spike" or surge...
>
> 5) What happens when the faucet tries to run for an hour at 30
gals/min,
> then 11 hours at 1 gal/min? Uh oh again. We were only able to run at 30
> gals/min for about 4-5 mins, and then the flow rate got cut back to 5
> gals/min for the rest of the hour. We really wanted 1800 gals to go
through
> the system during that hour, but it actually took 6 hours to get all 1800
> gallons through; too bad...
>
> Sorry for the silly analogy, but that's how my brain works...
>
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com>
> Sent: Tuesday, October 29, 2002 9:58 AM
>
>
> Russ:
>
> We're using EMC Clariion disk arrays. These are using EMC's version
> of RAID-5; they call it RAID-S. There is 2GB of cache if front of
> the disks. They claim that the cache is write guaranteed so that
> we'll never lose an update. So far, so good, and the performance
> has been acceptable, except (you knew this was coming, huh?) when
> we do large file moves from one tray to another, or when doing a
> refresh of our SAP stage system. This activity kinda buries the
> internal bus as well as the fiber, so that other users suffer.
>
> I guess to make a short answer even longer, this RAID-S technology
> seems to work a lot better than RAID-5 used to.
>
> Remember, though, YMMV.
>
> Cheers,
> Mike
>
> -----Original Message-----
> Sent: Monday, October 28, 2002 5:24 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Hi,
> I just got forwarded a whitepaper from Hitachi and Oracle, that compairs
> raid 5+ and raid 1 using the TPC-C benchmark test suite. The claim is
that
> raid 5 is as fast or faster. While I'm waiting for a comparison or raid
5+
> with raid 0+1, I thought I'd take a poll with the list. The benchmark is
> using the Hitachi 7700E.
> Has anyone heard other recommendations attributed to Oracle that are
> pushing raid 5+ as the configuraton for "unrivaled performance"? Has new
> disk technology changed the general conception that raid 0 or 0+1 provides
> better performance than other raid levels?
>
> Thanks,
> Russ
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Brooks, Russ
> INET: Russ.Brooks_at_dayzim.com
>
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Yechiel Adar
  INET: adar76_at_inter.net.il

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Received on Wed Oct 30 2002 - 10:44:20 CST

Original text of this message

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