From: Bruce Momjian <bruce@momjian.us>
Message-Id: <200708270011.l7R0Bw114136@momjian.us>
Subject: Re: Block size with pg_dump?
In-Reply-To: <46D1F213.4010107@verizon.net>
To: Jean-David Beyer <jeandavid8@verizon.net>
Date: Sun, 26 Aug 2007 20:11:58 -0400 (EDT)
CC: pgsql-sql@postgresql.org
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="US-ASCII"

Jean-David Beyer wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> When I make a backup of a database, I put the output file directly on
> magnetic tape; i.e., my command looks like this:
> 
> pg_dump --file=/dev/st0 ....
> 
> This way I do not have to worry if the total backup exceeds the size of a
> file system, and it saves me the trouble of copying it to the tape as a
> separate step. My current tapes will hold 20 GBytes raw or 40GBytes if I
> enable hardware compression (assuming 2:1 compression happens). Now it says
> in the documentation that if I use format c it will compress the data in
> software, so I doubt the hardware compression will do much.
> 
> I do not know what blocksize pg_dump uses, or if it insists on a particular
> blocksize on input.
> 
> Now my tape drive will work with any blocksize, but prefers 65536-byte
> blocks. I do not see any options for this in pg_dump, but I could pipe the
> output of pg_dump through dd I suppose to make any blocksize I want.
> 
> On the way back, likewise I could pipe the tape through dd before giving it
> to pg_restore.
> 
> Does pg_dump care what blocksize it gets? If so, what is it?

I assume you could pipe pg_dump into dd and specify the block size in
dd.

-- 
  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +