Re: RAID + LUKS + LVM performance

[david]

On Thu, 11 Mar 2010, Matthias Schniedermeyer wrote:

> 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.

linux software raid (the md tools) support linear or striped modes for 
raid0, so what you are looking for is available.

however I think that defeats part of the OPs purpose, which was to try and 
spread the I/O across all 4 partitions to be able to use multiple cores 
for the encryption.

David Lang
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