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Date:      Thu, 24 Jan 2013 15:24:37 +0100 (CET)
From:      Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To:        Adam Nowacki <nowakpl@platinum.linux.pl>
Cc:        freebsd-fs@freebsd.org, freebsd-hackers@freebsd.org
Subject:   Re: ZFS regimen: scrub, scrub, scrub and scrub again.
Message-ID:  <alpine.BSF.2.00.1301241523570.5666@wojtek.tensor.gdynia.pl>
In-Reply-To: <51013345.8010701@platinum.linux.pl>
References:  <CACpH0Mf6sNb8JOsTzC%2BWSfQRB62%2BZn7VtzEnihEKmEV2aO2p%2Bw@mail.gmail.com> <alpine.BSF.2.00.1301211201570.9447@wojtek.tensor.gdynia.pl> <20130122073641.GH30633@server.rulingia.com> <alpine.BSF.2.00.1301232121430.1659@wojtek.tensor.gdynia.pl> <51013345.8010701@platinum.linux.pl>

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> then stored on a different disk. You could think of it as a regular RAID-5 
> with stripe size of 32768 bytes.
>
> PostgreSQL uses 8192 byte pages that fit evenly both into ZFS record size and 
> column size. Each page access requires only a single disk read. Random i/o 
> performance here should be 5 times that of a single disk.

think about writing 8192 byte pages randomly. and then doing linear search 
over table.

>
> For me the reliability ZFS offers is far more important than pure 
> performance.
Except it is on paper reliability.



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