From: Greg Smith <greg@2ndquadrant.com>
To: Jesper Krogh <jesper@krogh.cc>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: jd@commandprompt.com, Scott Marlowe <scott.marlowe@gmail.com>
Cc: Steve Crawford <scrawford@pinpointresearch.com>
Cc: pgsql-performance@postgresql.org, Ben Chobot <bench@silentmedia.com>
Subject: Re: BBU Cache vs. spindles
Date: Sun, 24 Oct 2010 13:04:45 -0400
Message-ID: <4CC4672D.9040401@2ndquadrant.com> (raw)
In-Reply-To: <4CC1BD86.8070006@krogh.cc>
References: <4CC04EA50200002500036C5E@gw.wicourts.gov>
<201010211935.o9LJZTM21744@momjian.us>
<4CC0513E0200002500036C68@gw.wicourts.gov>
<4CC1094C.1090306@2ndquadrant.com>
<13038.1287720327@sss.pgh.pa.us>
<4CC1AFB3.3000903@2ndquadrant.com>
<4CC1BD86.8070006@krogh.cc>
Jesper Krogh wrote:
> Can you point to some ZFS docs that tell that this is the case.. I'd
> be surprised
> if it doesnt copy away the old block and replaces it with the new one
> in-place. The
> other behaviour would quite quickly lead to a hugely fragmented
> filesystem that
> performs next to useless and ZFS doesnt seem to be in that category..
http://all-unix.blogspot.com/2007/03/zfs-cow-and-relate-features.html
"Blocks containing active data are never overwritten in place; instead,
a new block is allocated, modified data is written to it, and then any
metadata blocks referencing it are similarly read, reallocated, and
written."
http://opensolaris.org/jive/thread.jspa?messageID=19264 discusses how
this interacts with the common types of hardware around: no guaratees
with lying hard drives as always, but otherwise you're fine.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services and Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, jesper@krogh.cc, tgl@sss.pgh.pa.us, Kevin.Grittner@wicourts.gov, bruce@momjian.us, scott.marlowe@gmail.com, scrawford@pinpointresearch.com, bench@silentmedia.com
Subject: Re: BBU Cache vs. spindles
In-Reply-To: <4CC4672D.9040401@2ndquadrant.com>
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