Question about setting up a RAID-0

[SleepWalkerX]

Could someone explain why hardware raid is better than software raid? What if I had got a 1X PCIe sata raid controller and put two sata2 drives on it. Each drive can be accessed up to 3Gb/s right? But the 1X PCIe lane only supports up to 5Gb/s. So basically isn't that as fast as the drives can be accessed, 5Gb/s? And if I had a motherboard with two sata2 ports and software raid is there anything stopping me from achieving 6Gb/s using software raid? Am I thinking about this wrong?

 

[Roguestar]

Pro tip: Don't RAID-0. :thumbsup:

 

[Blain]

RAID 0 with 4 HDs is the greatest thing since sliced bread.
Those that say otherwise are simply jealous.

 

[MerlinRML]

Originally posted by: SleepWalkerX
Could someone explain why hardware raid is better than software raid? What if I had got a 1X PCIe sata raid controller and put two sata2 drives on it. Each drive can be accessed up to 3Gb/s right? But the 1X PCIe lane only supports up to 5Gb/s. So basically isn't that as fast as the drives can be accessed, 5Gb/s? And if I had a motherboard with two sata2 ports and software raid is there anything stopping me from achieving 6Gb/s using software raid? Am I thinking about this wrong?

Hardware RAID means that you've got a dedicated processor to do your RAID parity calculations for you. Software RAID means that you're using some software (usually fairly tightly coupled to your OS) to manage your RAID arrays and using the host CPU to do your RAID parity calculatiosn. Hybrid RAID also called driver RAID or fakeRAID uses a piece of hardware to manage your RAID arrays but still uses your host CPU to do RAID parity calculations. RAID 0 and RAID 1 (plus their tiered variations) do not do parity calculations. RAID 3-6 do.

Hardware RAID has the added benefit of not being integrated into your motherboard. It may have dedicated memory as a cache, and that cache may be battery backed up.

Some things to remember when doing performance calculations.
1) Real disk performance is much lower than SATA/SAS interface bandwidth.
2) Just because something is integrated into the motherboard, doesn't mean there isn't some bandwidth being dedicated to it. I believe most Intel desktop chipsets get 4x PCI-E lanes between the northbridge and southbridge.
3) The fastest SAS drive I've seen today is capable of approx. 115MB/sec sustained sequential throughput. All other mechanical SAS/SATA drives are going to be slower.
4) 1x PCI-E lane is going to be roughly 250MB/sec of realworld bandwidth in each direction
5) PCI-E 2.0 or gen2 is now available. That will double the bandwidth figures I've already mentioned if you're using it.

So yes, your calculations are correct in that you've oversold your theoretical bandwidth. In the real world, you'll not need to worry about it.

 

[JackBurton]

Originally posted by: Roguestar
Pro tip: Don't RAID-0. :thumbsup:

 

[Zepper]

But if you decide to do RAID 0 anyway, despite the sage advice given above - back up, back up, back up - for god's sake, back up!!! "Running RAID 0 without a good, verified backup is like flying experimental aircraft without a parachute." (c) by me sometime around 2002-2003. Everyone on the AT Forums should be backing up anyway having read numerous sob stories (one on the first few pages of GenHard right now), but moreso on RAID 0.

.bh.