Message-ID: <467BD479.5090603@commandprompt.com>
Date: Fri, 22 Jun 2007 06:54:01 -0700
From: "Joshua D. Drake" <jd@commandprompt.com>
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To: Toru SHIMOGAKI <shimogaki.toru@oss.ntt.co.jp>
CC: Steve Atkins <steve@blighty.com>,
	PostgreSQL Performance <pgsql-performance@postgresql.org>
Subject: Re: PITR Backups
References: <7E0807EE-B970-4869-A248-B838E42AD9EE@hi5.com>
	<9761.1182472005@sss.pgh.pa.us> <467B3459.9030808@oss.ntt.co.jp>
	<B4AE85C4-8E1C-4EF6-B8A4-7B66C26238EA@blighty.com>
	<467B7A89.3080300@oss.ntt.co.jp>
In-Reply-To: <467B7A89.3080300@oss.ntt.co.jp>
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Toru SHIMOGAKI wrote:
> 
> Steve Atkins wrote:
> 
>>> - When we take a PITR base backup with hardware level snapshot operation
>>>   (not filesystem level) which a lot of storage vender provide, the 
>>> backup data
>>>   can be corrupted as Dan said. During recovery we can't even read it,
>>>   especially if meta-data was corrupted.
>>
>> I can't see any explanation for how this could happen, other
>> than your hardware vendor is lying about snapshot ability.
> 
> All of the hardware vendors I asked always said:
> 
>  "The hardware level snapshot has nothing to do with filesystem 
> condition and of course with what data has been written from operating 
> system chache to the hard disk platter. It just copies byte data on 
> storage to the other volume.

Right that has been my understanding as well.

Joshua D. Drake

> 
> So, if any data is written during taking snapshot, we can't assurance 
> data correctness *strictly* .
> 
> In Oracle, no table data is written between BEGIN BACKUP and END BACKUP, 
> and it is not a problem REDO is written..."
> 
> I'd like to know the correct information if the explanation has any 
> mistakes, or a good way to avoid the probrem.
> 
> I think there are users who want to migrate Oracle to PostgreSQL but 
> can't because of the problem as above.
> 
> 
> Best regards,
> 


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