I'm interested in running a RAID 5 array on my next machine. Most motherboards have built in RAID controllers these days that will support this. However, what are the trade offs between the built-in controllers and the stand alone cards? When do you need a stand-alone card and when is a more simple motherboard controller sufficient?

I don't have a lot of practical experience with RAID and I've had a hard time finding straight forward answers to the differences, trade-offs, and features of different types of controllers and the applications to which they're best suited. I'm interested in a RAID 5 array because I'm looking for a balance between performance, storage efficiency, and data redundancy. Also, controllers supporting RAID 3 seem to be rather uncommon.

1/9/2009 1:11:16 PM

well for one, motherboard RAID isn't supported in linux until after you install making it near impossible to install the OS on the array. hence why a lot of linux folk call it fakeraid. Windows has no problem with this.

motherboard RAID is also software RAID as the only thing it does is supports building the array outside of the OS (typically you can't format or partition), using it's own BIOS chip, but aside from that, the processing is done via the CPU and managed in the OS, whereas with hardware it's dedicated and you can build/format the array outside of any OS environment and is a lot less susceptible to data loss if anything goes wrong with the OS.

[Edited on January 9, 2009 at 1:24 PM. Reason : .]

1/9/2009 1:23:31 PM

http://en.wikipedia.org/wiki/RAID#Firmware.2Fdriver-based_RAID

fake raid ftl

Quote :

"well for one, motherboard RAID isn't supported in linux until after you install making it near impossible to install the OS on the array."

Not true. A driver disk can be used in linux just as it can during a windows install. Keep in mind that they have to be linux drivers/modules that the hardware vendor has to write. If they don't provide any for their hardware, then that's their problem, not linux's.

1/9/2009 1:23:35 PM

ok, that's fair. but most major manufacturers do not do this. in fact most defer to the linux community to write their own. so typically you can't.... unless you can write your own hardware drivers.

Quote :

"Disclaimer used on Gigabyte's motherboard pages for SATA RAID: Due to different Linux support condition provided by chipset vendors, please download Linux driver from chipset vendors' website or 3rd party website. "

and i've never seen Intel write a linux driver for their matrix RAID solutions, (other than RAID 0/1), no RAID 5/10/0+1 support, no driver other than for kernel 2.4

from Intel:

Quote :

"Please contact your Linux distribution vendor directly with questions or for more information. You should contact your Linux distribution vendor for support."

so that's why i say it's near impossible. most current OS's use 2.6 or higher, and most of the time people are going to use RAID 5 in a server setup

fwiw, i installed windows 2008 server in RAID 5 on an intel chipset with no issues, no disks, the on-board RAID was pretty much transparant to Windows... the only thing i had to do was install the intel matrix RAID management software after Windows install

[Edited on January 9, 2009 at 1:39 PM. Reason : .]

1/9/2009 1:29:39 PM

How the hell do your sort out the hardware RAID cards from the software RAID cards? Are there even hardware RAID cards available for less than $300?

1/9/2009 2:36:11 PM

Quote :

"Are there even hardware RAID cards available for less than $300?"

not decent ones, no

software raid is slower than hardware raid, yes, but i doubt you'll really notice the difference.

in order of speed, it goes raid 0 > raid 1 > raid 5 (this, of course, is completely dependent on the number of spindles you have in each array)

1/9/2009 2:56:12 PM

look for on-board memory, it's one thing to look for to make sure data isn't lost (or corruption) if the system shuts down unexpectedly

Quote :

"in order of speed, it goes raid 0 > raid 1 > raid 5"

i thought it was 0, then 5, then 1 for read.

you're probably right though in terms of write speed.

[Edited on January 9, 2009 at 3:02 PM. Reason : /]

1/9/2009 2:57:56 PM

^again, it depends on # of spindles

1/9/2009 3:07:40 PM

Quote :

"look for on-board memory, it's one thing to look for to make sure data isn't lost (or corruption) if the system shuts down unexpectedly"

no, on-board memory doesn't prevent data corruption. on-board memory is used for read and sometimes write caching.

If you want to use RAID controller memory for write-caching and want to be sure to avoid data loss/corruption, then you also need a backup battery for the RAID card and disable write-caching in the disk drives themselves. the backup battery allows the cached data to remain in memory for X hours so it can be written to disk once power is restored in case of power loss.

Most decent hardware RAID cards cost at least $300, and the backup battery for it is usually around $100 as well.

if you really want a hardware RAID card for home use, a good budget card might be the Adaptec 2405. it has an 800mhz proc, pci-e, etc. just make sure you order the one with the special cable. caveat - it doesn't support RAID5. only RAID0/1/10. RAID10 requires 4 disks.

1/9/2009 4:23:38 PM

^ah good call, forgot to mention the battery

1/9/2009 4:30:11 PM

I don't have the budget the justify the storage inefficiency of RAID 10.

1/9/2009 5:09:55 PM

The Areca ARC-1210 is by far the best consumer level hardware RAID card you can get. I consistently get ~300MB/s sustained reads and bursts up to 750MB/s on my RAID5 array that consists of 4 single platter 320GB WD3200AAKS drives. The support can be a little spotty if you need to get someone on the phone, and the management interface leaves a bit to be desired, but it hauls ass. Much better than most 3ware and equivalent cards.

http://www.newegg.com/Product/Product.aspx?Item=N82E16816131003

1/9/2009 10:54:18 PM

^ Any experience using that card with the new Intel i7 chipsets?

1/10/2009 1:33:33 PM

Controller cards are better, because you can move them from machine to machine. If you're with motherboard RAID 5, you will probably have to rebuild the partition; especially if you're not experienced with RAID. Moving a RAID array on a controller card is as usually as simple as moving the card and HDs, and making sure the HDs plugged in the same order.

What I have done since 2002 is this: I have 2 RAID partitions. One for mirroring, using an older pair of HDs, and one for striping, using a newer pair of HDs. After a few years I retire the older pair (they're probably small by then), move the striped to mirrored, and buy 2 new disks for striping. Whenever I have data, I can usually tell if it's speed-critical (program files) or integrity-critical (my documents, etc). There are few situations where you need both speed and integrity on a personal computer; so this way I get the best of both worlds, and have a plan for future upgrades.

1/11/2009 4:45:41 PM