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Re: tablespaces and DB administration

From: pgsql(at)mohawksoft(dot)com
To: "Andreas Pflug" <pgadmin(at)pse-consulting(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: tablespaces and DB administration
Date: 2004-05-28 12:40:16
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Lists: pgsql-hackers
> pgsql(at)mohawksoft(dot)com wrote:
>>What you are missing is that the RAID is dealing with the multiple drives
>>as one drive. Two operations have to happen serially,
> You're kidding or vastly underestimating raid controllers. The average
> db access is well served with a single block of data, stored on a single
> drive. Nicely parallelizable by a raid controller if it has a minimum of
> smartness.

The data contained on a RAID is spread across all the drives in the raid,
is this not true?

To access data on a drive, one must get the data off all of the drives at
the same time, is this not true? (yes there is flexibility with mirror and
ignoring parity on reads)

If you perform two different operations on the RAID, you must access each
RAID drive twice.

If you perform different operations on multiple different drives, you can
access the same amount of data as you would with the RAID, but have
parallelized operations.

This is a fact. It is *the* drawback to RAID system. If you do not
understand this, then you do not understand RAID systems.

Perform any benchmark you want. Take any RAID system you want. Or,
actually, I have a factual reason why RAID systems perform worse than
multiple single drives, I have written a quick program to show it. I have
even double checked on my own RAID system here. Now, your turn, show me
some facts that support your position, not just that "it should." Show me
how it can, show proof as to how a RAID system can be faster than its
component disks.

If you can't, I'm pretty sure I can safely ignore this part of the thread.

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