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The Ubuntu wiki page on FakeRaid says the following:

[A] number of hardware products ... claim to be IDE or SATA RAID controllers... Virtually none of these are true hardware RAID controllers. Instead, they are simply multi-channel disk controllers combined with special BIOS configuration options...

Is there a typical way to identify (from a product specification) whether a motherboard has "real" RAID, or are "real" RAID products generally unavailable to consumers?

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5 Answers

up vote 24 down vote accepted

The market for RAID controllers is fairly much consolidated these days. Three broad brush heuristics can be applied:

  1. Price. Take a look at the pricing for genuine RAID cards from Areca, 3Ware, Adaptec and LSI. Anything that is much, much cheaper than these controllers is a 'fake RAID'. Remember, if it's too good to be true it probably isn't.

  2. There are a fairly limited number of manufacturers these days who actually make pukka RAID controllers. Chances are that something not made by one of the main manufacturers of such kit is a 'fake RAID'. The main outfits that make RAID controllers are: Adaptec, LSI, Areca, Intel and Highpoint (possibly one or two others that I can't recall off the top of my head).

  3. The main outfits that produce these cards will also document the specifications in some detail on their web sites. If you can't find a detailed specification for the card get something you can get such a spec for. Note that not all cards produced by these outfits are necessarily RAID controllers, but the specs on the web site should make this clear.

  4. Thanks to sh-beta for pointing this out: Hardware RAID controllers will also have the option of a battery backed cache. 'Fake RAID' controllers have no cache RAM, using the machine's main RAM as a cache.

Note that IBM, Dell, HP and other server manufacturers also sell RAID controllers. In many cases these are rebadged components made by Adaptec or LSI.

If you want to buy a RAID controller on the cheap, identify some specific models of appropriate specification from various manufacturers' current and immediately previous generations. Then search for that particular model on ebay and get it secondhand.

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One addendum: if it you have the option to add onboard battery-backed memory to the card, it's real RAID. And if you don't add the battery-backed memory, it's time to question why you want hardware RAID instead of software. –  sh-beta May 18 '09 at 0:41
    
+1 just for using the word pukka :) –  MarkR May 18 '09 at 13:48
    
From personal experience, Areca cards might be real RAID... But any card that can crash and require a server powercycle to reboot (not a soft reboot) is mighty annoying. They were also highly temperature sensitive. A 5-10 degree rise in computer room temperature (like when transferring to city water supply on the A/Cs) will crash them... Requiring a hard reboot. –  Alexandre Carmel-Veilleux Jun 10 '09 at 20:13
    
Never used Areca cards, mainly Adaptec, LSI and a couple of host based F/C RAID cards from Mylex and ICP-Vortex –  ConcernedOfTunbridgeWells Apr 8 '11 at 13:45
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Look for mentions of "Host RAID" or "software RAID". Not all fake RAIDs are labelled with one of those, but it'll catch probably 90% of them. There are very few motherboards with (decent) RAID controllers built-in, though. Your best bet is to buy a decent add-on RAID card, or just use software RAID. It's not much slower (except compared to battery-backed RAID cards, which are a whole other world) and it's a million times easier to manage, and more flexible.

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Many "fake" RAID controllers work without any special software as their BIOS masks this, in practice impersonating a dedicated RAID controller CPU, so software alone is probably not going to give you enough hints.

Also, and this is a bit interesting - "fake" (host-based) RAID controllers can easily be much faster than many "true" RAID controllers due to today's CPU speeds being what they are. Of course, the price for this is that you're losing valuable CPU time you could've used for something else - and this is mostly what a "real" RAID controller will fix for you - but be prepared to pay a lot if you want anywhere near decent performance.

There are other things than performance to look for though, like stability, working hot swap, rebuild-speed that doesn't slow everything to a halt, on-line raid level migration and a battery-backed write-cache.

On consumer/enthusiast-oriented motherboards, built-in RAID are common as both types but... The normal host-based stuff like Intel ICH10 and so on are pretty damn fast, depending on the host speed of course - but it's not like it's doing anything you couldn't do with the OS alone (except booting off something more advanced than a mirror).

The cheap "real" RAID controllers on these motherboards are often some truly sad pieces of shit meant for simple and trouble-free mirroring. These mostly perform badly and lack any of the normal features like a decent cache or battery. Stay away from them and never use them for performance-means. They're often weirdly labelled like "SuperDrive" or "EasyRaid" or whatnot and use slow, simple chips for the RAID processing.

As other answers already indicate, a non-fake RAID controller in the context meant does cost a bit - but should be easily identified on this alone. But almost all controllers do at least some host-based processing as well - it's just a matter of how much (or little) and how fast their dedicated CPU/s is/are.

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Generally if your RAID system NEEDs software to work then it's not a proper RAID controller, at least in my mind. The good ones do everything they need in BIOS/pre-boot.

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Ummm, all disk controller need software — device drivers — to work. It may or may not come with your OS, but its there. –  derobert Jun 13 '09 at 4:35
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not the case sorry, HP's very well regarded 'SmartArray' controllers do not need drivers on pretty much any OS as they present themselves as a regular disk controller and all confit can be completed via a BIOS menu. –  Chopper3 Jun 13 '09 at 6:02
    
Come off it! Even a regular disk controller needs a driver. The driver might well be built into the OS, but even a standard IDE contorller needs a driver. –  Richard Gadsden Jul 20 '09 at 14:02
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You're missing the point, the key here is that most decent hardware RAID controllers will present a hardware-managed array as a single disk, using a non-feature-rich 'standard ATA controller' BIOS presentation - i.e. one that emulates a single disk on the most basic disk controller imaginable. These semi-RAID systems will often present all of an array's disks to the BIOS if the drivers aren't in place, i.e. the driver is doing some of the work. –  Chopper3 Jul 20 '09 at 15:32
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That's simply not the case, try any of Compaq/HP's SmartArray controllers for instance, you setup the RAID array via the BIOS then the OS just sees them as a single disk off a regular ATA disk controller - no drivers needed. Of course most people load the drivers as they give you better performance, error alerting, live array reconfiguration etc. but crucially you don't NEED the drivers. –  Chopper3 Nov 25 '09 at 8:41
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HP seems to use both "fake RAID" (ICH9R) and "pukka RAID" (add-in cards) in their servers. I have been in touch with both kinds; let me tell you: Pay the extra buck for the "real RAID" card. If you choose wisely, you'll have a good card that lasts longer than just one motherboard.

On the other hand, I believe there is a third RAID "type": software RAID (as in Linux). I've been a happy user of a few software RAID Linux boxes for some time now, and I've been very pleased with them. Mostly by the fact that one can re-arrange the raid using a live CD and a computer with enough SATA ports! Been there, done that!

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