linux-kernel - Re: RAID + LUKS + LVM performance

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Message-ID: <20100311173604.GA17659@citd.de>
Date:	Thu, 11 Mar 2010 18:36:04 +0100
From:	Matthias Schniedermeyer <ms@...d.de>
To:	Mathias Buren <mathias.buren@...ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: RAID + LUKS + LVM performance

On 11.03.2010 13:08, Mathias Buren wrote:
> 
> Hi,
> 
> (please cc me as I'm not subscribed)
> 
> I've a friend who's going to set up a fileserver consisting of 8x 1.5TB
> HDDs, an 8-port PCI-E RAID card (Areca ARC-1220 @
> http://www.areca.com.tw/products/pcie.htm ) etc.
> The plan is create a RAID5 array spanning all the disks, then create 4
> partitions. These 4 partitions would be encrypted using LUKS (Twofish or
> AES256).
> These 4 encrypted partition would be set up in RAID0 using Linux' software
> (mdadm), then LVM would be used on top of that (one big PV, one big VG and
> a big LV or so).
> 
> The reason for this is that kcryptd is not multithreaded (afaik). By having
> 4 encrypted partitions, then md0 on top of them, I'm forcing 4 kcryptd
> processes to run on all four cpu cores whenever something is written to the
> disks, which should improve (encryption) performance.
> 
> Is this a good way of doing it, or is there a smarter way?

The setup you describe would only work with SSDs. HDDs would seek 
themselves to death.

The problem is the RAID-0 over the 4 partitions. At that point you would 
need, instead of the 4 partitions, something that is round-robin. So 
that the mapping of the (physical) blocks from the upper to the lower 
would be effectivly linear/unchanged.

AFAIK something like that is (currently) not possible.





Bis denn

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