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The old raw devices chestnut.

From: Jim Smith <jim_at_jimsmith.demon.co.uk>
Date: Mon, 12 Apr 2004 08:54:08 +0100
Message-ID: <dS4PuczgskeAFwJq@jimsmith.demon.co.uk>


Note the cross-posting - but no flame wars please.

This question was prompted by a thread on the a postgres mailing list during which someone (Gregory Williamson) claimed

<quote>

raw devices, at least on Solaris, are about 10 times as fast as cooked file systems for Informix.
<quote>

This made me think about the old arguments, and I wondered about the current state of thinking. Some of my knowledge will be a bit out of date.

Oracle: (my main experience)
At various times Oracle have claimed (talking to consultants, not marketers) that raw devices are 5-20% faster than filesystems. This may vary on the current state of the oracle code and/or the filesystem being compared against. Veritas seem to agree by producing QuickIO for Oracle, claiming "performance of raw with the management of filesystem".

I have never been sufficiently convinced to implement a major system with raw.

Sybase: (some experience)
Sybase claim filesystems are faster, because of OS buffering, but unsafe for the same reason. They only ever suggest filesystem for tempdb. They don't seem to have heard of fsync()[1]

DB2:
No idea

Informix:
No idea beyond the claim which started this off.

What is the latest thinking, both in terms of vendor claims and practical experience?

[1] or whatever system call forces write-through caching

-- 
Jim Smith
Because of their persistent net abuse, I ignore mail from
these domains (among others) .yahoo.com .hotmail.com .kr .cn .tw
For an explanation see <http://www.jimsmith.demon.co.uk/spam>
Received on Mon Apr 12 2004 - 02:54:08 CDT

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