[CentOS] settings up cheap a NAS / SAN server, is it possible?

David Mackintosh David.Mackintosh at xdroop.com
Mon Jun 30 17:06:06 UTC 2008

On Sun, Jun 29, 2008 at 09:08:15AM +0200, Rudi Ahlers wrote:
> Hi all
> I want to look at setting up a simple / cheap SAN / NAS server using 
> normal PIV motherboard, 2GB (or even more) RAM, Core 2 Duo CPU (probably 
> a Intel 6700 / 6750 / 6800) & some SATA HDD's (4 or 6x 320GB - 750GB). 
> My budget is limited, so I can't afford a pre-built NAS device.
My own experience: I have done two NAS systems using CentOS.  One is
a HP DL585G1 with four 300GB drives using a hardware RAID-5.  The
second is a Dell PowerEdge 2600 with four 300GB drives (software
raid-10) and two 32GB drives (software raid-1).  

One has a multi-core Opteron processor, the other has a high-end
Xeon processor with HT disabled.  Both have 2GB of RAM.

Both are used by high-demand compute processes as NFS servers.

Despite a lot of fidding, configuring, testing and tuning, neither
result is very good when it comes to NFS performance.  We've gone
so far as to run everything as noatime (ie local mount, nfs export,
and nfs client mount) hoping for better performance.

In comparing the systems we tried the hardware-RAID5 first on the 
assumption that HW-Raid5 is faster than SW-Raid, for a higher yield
than Raid-10.  However we don't think that the elevator used in the
kernel makes intelligent stepping decisions on the HW-Raid5 because
it doesn't see the "real" geometry of the disks involved, only the
aparrent geometry of the RAID5 disk.

The Software-Raid10 is better in some ways because the kernel sees
the real disk geometries.  Performance is about on par with the 
other computer, even though the other computer has the better CPU.

Due to the hardware involved I couldn't try Solaris 10, but we have
had experiences in the past where the NFS server on Solaris was
significantly better than the NFS server in CentOS/RedHat, both in
terms of throughput and perceved latency under load.

If I was doing it again, I'd push harder for a budget for a NetApp
filer.  For what we are attempting to do, you get what you pay for.

If I was doing it again with the budget restrictions, I'd probably 
try Solaris with software raid.  I would then try the *BSD family,
but only after Solaris because I have extensive Solaris experience.

/ /()\ \ David Mackintosh | 
         dave at xdroop.com  | http://www.xdroop.com
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