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If performance is not a issue what makes hardware raid better then software raid. so far i have drawn the following conclusions.

Hardware raid is limited to the raid controller if that pacs up you need another of the exact raid controllers, Where as if your server or OS pacs up with software raid you can switch all the disks to another computer and use the exact same OS.

What are your guys view on the matter since so far thats the only benefit of hardware raid that i have found out.

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Keep in mind that some of the new filesystems (ZFS, and someday BTRFS) solve some of the problems which occur with older software RAID methods. The "Copy on Write" and "full-stripe writes" features in ZFS ensure that the data is written to the disk atomically, which means that a battery backed cache (and therefore, a hardware RAID card) isn't always necessary. –  Stefan Lasiewski Jul 20 '11 at 21:38
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There are two major benefits to hardware RAID:

  1. Performance. If that's not a consideration, don't consider it.
  2. Battery-Backed Cache.

2 really goes hand-in-hand with 1, but it also plays a role from a data integrity standpoint: Let's consider two identical machines, one with Software RAID, one with a battery-backed hardware RAID, both with write cacheing enabled.
If we write a whole bunch of data to these two machines, then rip the plug out of the wall before the data is sync'd to disk (by the OS on the software RAID box, or the controller on the hardware RAID box), we now have two different scenarios:

The Hardware RAID machine will, when power is restored, see that there are writes in the cache, spin up the drives, sync the data to disk and move on with its life.

The Software RAID machine will, when power is restored, reboot normally. Since the system RAM lost power the writes that were stacked up waiting to be flushed out to disk are gone forever. The results here could range from inconvenient (a little data loss) to catastrophic (the partition table has been eaten, vital irreplaceable data has been left in a half-written, corrupted state, etc.).

Now that I have portrayed the nightmare scenario, consider the likelihood of it happening. Presumably your server is on a UPS, ideally with redundant power supplies fed from different UPS circuits. The chance of a catastrophic failure in that scenario is relatively low, and you may be fine trusting software RAID here.
In exchange for taking that (theoretically small) risk you aren't beholden to a particular brand of controller and revision of the controller firmware in the event something goes horribly wrong, and you have the flexibility afforded you by software RAID (which often includes mirroring only part of a drive, or being able to mirror across drives of different sizes, spindle speeds, etc. -- Possibly a consideration if you have Frankenstein hardware).

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ye thing is that i got 2 huge UPS with battery packs that should last a hour and then onsite generators that take 15 min to kick in, so ye it is a small/medium sized business so we looking to reduce costs on a new file server i mean user's dont need to access data at lightning speeds so performance is not a issue and we have daily rotating bakcups aswell as ounce a week we swap out a nas that gets backed up at the managers house to another nas =D just trying to make a final decision, thanks for your input –  Ludjer Jul 20 '11 at 21:13
Reducing costs? Hardware raid is going to cost what another £300 on the cost of a server, over a 5 year life they're saving £60 a year? Is it worth it to save £500? –  ITHedgeHog Jul 20 '11 at 21:18
@ITHedgeHog - It actually can be a substantial cost savings - Our analysis servers can't be virtualized (they're CPU-Heavy), but don't really need fast disks, just fault-tolerance in case one fails. We build them with software RAID and tiny slow hard drives to the tune of about USD$400 less per box. Build five machines and the 6th is effectively free :-) –  voretaq7 Jul 20 '11 at 21:28
well the cheapest raid card i can get is 500Euro unless i ship got a very small selection that i can use since i live in south Africa. And also that 500 Euro could be to more ram or hard drives or upgrading the CPU to take on the extra task. I really currently dont see unless you got a huge budget to spend why small companies would go for hardware raid unless there going for Branded servers that come with raid cards. –  Ludjer Jul 21 '11 at 7:00
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Your question basically encapsulates my philosophy.

I prefer hardware RAID controllers in "enterprise" deployments. If I know I'm going to have warranty, spares availability, and vendor support I'd typically rather have the performance and features of hardware RAID.

In small business scenarios where the likelihood is that the Customer is going to let support lapse I'd rather take the (increasingly very slight) performance "hit" and go with software RAID (typically RAID-1 in small businesses I work in, anyway). This is typically cheaper than a hardware solution. In the end, I'd rather have some kind of protection against disk failure than none at all.

As you say, with software RAID I know I'll be able to read the disks using the same software RAID implementation on any other computer without a special controller. Typically the Customer isn't pushing the performance envelope of their server and doesn't need fancy features so they end up losing nothing and gain some ability to recover in the event of catastrophic failure of the server computer.

Software RAID performance has gotten quite good in the last few years, but I've been using it in small deployments all the way back to Windows NT 4.0 with good results. It's a cheap insurance policy.

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thanks for your input i am working in a small business environment so i was thinking software raid is the way to go. –  Ludjer Jul 20 '11 at 21:15
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