Re: Advice: Hardware vs. Software RAID5
On Tue, Jan 15, 2008 at 06:24:52AM -0800, tofu.oni@gmail.com wrote:
> I'm looking for general advice/tips/admonitions of doom. I'm getting
> ready to build a file server and I want to have some data redundancy.
> I've ordered four 350G SATA drives and I plan to put them into some
> kind of RAID 5 configuration. The boot disk will be a separate IDE
> drive.
>
> The motherboard I'm using is an intel d945gnt. It has an intel Martix
> driver that will let me do RAID 5 in the bios. Then, linux should see
> one big whopping device. That sounds like the easiest solution to me.
>
> Option two is to use linux software RAID. I've never done that
> before, but I can learn.
>
> So, please help me to make a decision. Thanks. (if it matters, this
> is just a file server for my home. I don't need super high throughput
> or anything like that)
Executive summary: Software RAID suits your needs better. Read on for
justification.
RAID provides reliability and/or better disk performance. It sounds like
you are saying that reliability is your primary goal, and disk performance
is not really relevant (though, of course, no one likes sluggish I/O).
Consider what reliability RAID provides: it's about whether your data will
survive various forms of hardware failure because the hardware is cheap and
easy to replace. Remember that the hardware RAID controller is hardware
that can fail. Worse, it's built into your motherboard so anything that
kills your motherboard (short circuit in the memory, CPU overheating, etc.)
also takes out your RAID controller. To be able to access your data you'll
need the same RAID controller (with varying degrees of "same" depending on
the specific product line). If Intel discontinues that controller series,
your data cannot survive the failure of the controller.
Software RAID does not perform as well as hardware RAID, in general, but
you can always find a box to install Linux on and plug your disks into.
Software RAID takes one possible hardware failure out of the equation.
Anyway, that's my justification for using software RAID.
Incidentally, you might consider RAID10 instead of RAID5, depending on how
much disk space you are willing to trade for reliability. RAID5 with four
350GB disks gives you 1050GB of space and the ability to survive a single
drive failure. RAID10 gives you 700GB of space and the ability to survive
one drive failure and a 2/3 chance of surviving a second failure. In either
case you do a bit better with a hot spare. Of course, if you really care
about your data you can do RAID1 with two hot spares. Personally, I haven't
filled 250GB of space, but I also haven't been ripping/downloading a lot of
CDs or DVDs.
--Greg
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