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Re: PITR Backups

From: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
To: Toru SHIMOGAKI <shimogaki(dot)toru(at)oss(dot)ntt(dot)co(dot)jp>
Cc: Steve Atkins <steve(at)blighty(dot)com>, PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: PITR Backups
Date: 2007-06-22 13:54:01
Message-ID: 467BD479.5090603@commandprompt.com (view raw or flat)
Thread:
Lists: pgsql-performance
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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Subject: Re: Database-wide VACUUM ANALYZE
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