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From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Peter Jeremy <peter@rulingia.com>
Subject: Re: ZFS regimen: scrub, scrub, scrub and scrub again.
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>> While RAID-Z is already a king of bad performance,
>
> I don't believe RAID-Z is any worse than RAID5.  Do you have any actual
> measurements to back up your claim?

it is clearly described even in ZFS papers. Both on reads and writes it 
gives single drive random I/O performance.