Re: [Hampshire] Drobo

On Sat, Mar 07, 2009 at 12:14:28PM -0000, Rob Malpass wrote:
> I saw a review of this [1] sort of black box RAID array on Click
> last week and in truth it's just what I'm looking for as a NAS -
> currently have several drives via a NSLU2 but making a backup of
> 100Gb+ takes ages. However at £430 odd quid for the array and
> another £190 for the ability to use it as a NAS - it's very pricey
> particularly considering the hard drives required would be extra....

> So it got me thinking about an equivalent DIY solution. I already
> have a few hard drives I could use but I have a few requirements:

> 1) I'd like the drives to be hot swappable like the Drobo

SATA will do that, provided you use modern drives and a reasonably
recent (last few years) SATA controller.

> 2) Not sure what version of RAID to go for - any adivce?

I use RAID-1 at the moment.

> 3) Presume I'd need a motherboard and case that could handle RAID.
> I'm very green here - is RAID a software thing i.e. any mobo with 4
> SATA ports can support it or is a special mobo required?

There's basically two ways of doing RAID. You can have hardware
RAID, where the data duplication (in the case of RAID-1) or parity
calculations (in the case of RAID-5/6) are off-loaded to the
controller hardware. This is typically expensive, particularly if
you want RAID-5 or -6.

The other method is to use software RAID, where the main host CPU
works out what data should get written to each disk, and despatches
the data accordingly. This is, obviously, much cheaper, as it doesn't
involve any custom hardware. On modern computers, the CPU overhead is
minimal.

Linux will do software RAID very well, using the mdadm tool.

Oh, and just to confuse the issue, there is a long and awkward
tradition of motherboard (and expansion card) manufacturers making
something with multiple disk controllers, and then writing
software-RAID functionality into their proprietary drivers, and
marketing the resulting device as "RAID". This is usually described as
fakeRAID (but not by the manufacturers trying to sell it to you). It
looks like hardware RAID, but it's not. You should expect to be paying
a premium for real hardware RAID, and if you're not, it's almost
certainly not hardware RAID but fakeRAID.

> 4) I'd need a case which allows hot swapping - or is it easier to
> just get 4 SATA caddies - one for each 5.25" drive bay?

There are any number of 4- and 5-bay eSATA cases on the market.
Some of them have one eSATA connector per drive, and thus will need
that many eSATA ports on the computer. Some of them contain port
multipliers, and only need the one eSATA cable to run all of the
drives.

I've got an EdgeStore DAS-501t[1,2], which has 5 bays, caddies, and
a port multiplier. It also comes with an eSATA PCI-E card (which I
didn't need, as my motherboard has an eSATA port on it already).

> 5) Is there a distro which makes this easy(er than others) something
> a la Smoothwall for firewalls? Ubuntu is my distro of choice but I
> have a feeling setting something low level like this up could well
> be very tricky. A lot of the stuff google has thrown up in this
> area seems to be out of date.

Not that I'm aware of.

> Overall - is this a feasible DIY project of should I just save my
> pennies and buy it whenever I can afford it?

You can run a basic RAID system with very little management
overhead. If you want the fancy autonomic management capabilties of
the Drobo, I'm not aware of any open-source software to do it for you
-- yet. If you can code in python, though, and are interested in
writing it, let me and/or popey know, as we've been batting around
some ideas in this area. :)

Hugo.

[1] http://www.edge10.com/digital_storage.php
[2] http://carfax.org.uk/node/52

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