Raid 0+1 v's Raid 5 - opinions and real world results ?

I'm looking at upgrading and this could play a bit role in what motherboard and drives I get.

The DFI DR series have the Sil' SATA chipset that offers Raid 5 (though I believe it is Sata1 - 150 rather than Sata2 - 300). I could theoretically get this and stick 3 drives on it (minimum for raid5) and get striping with parity, which is generally agreed to be the best variant of Raid.

The lesser boards I am looking at , do have the option Raid 0+1. Does anyone have experience of this ? What sort of real worls results did you have if you did or do use it ?

Drive wise, I guess I'd be looking at 2 raptors in raid 0+1 or 3 large 7200rpm 16mb cache drives in raid 5. Similar price but obviously a large difference in storage capacity.

Thanks
mj

Generally the onboard RAID 5 offerings are actually done through software rather then hardware, and thus load your CPU.

Write performance will be poor. I cant remember what read performace is like tbh.

If you really want to go RAID 5, you should seriously invest in a dedicated hardware controller.

from what i knew a couple of years ago (might well still be true) a separate controller is best..

0+1 needs 4 drives, and gives you the capacity of 2, the speed of double one drive. raid 5 with n drives (n>2) gives you the capacity of n-1 drives, the speed of (n-1)x the speed of one drive, and resilliance.

0+1 gives you slightly more resiliance (in case 2 drives die) but the chances of this happening are pretty slim, and if 2 particular drives die, you'd still loose the array...

disclaimer : may be wrong :)

Real world performance? Not a lot. Raid 5 will have slower write performance if using the onboard controller. Striping will be faster much faster according to benchmark progs, but you won't notice that much, and mirroring is great for stuff if a single drive goes, but won't protect you if you are burgled or your computer is fried by lightning.

Nox

With all the posts on how great hardware RAID is compared to onboard stuff - what's a good one to go for? All i'd need is two-channel, maybe four if afordable, and i'd prolly stick with striped.

Recommendations?

RAID0,1 will be pretty much the same for both high-end and low-end cards.

RAID5,6 is what price matters. Cheap software cards/chips use software to handle raid (and its not well-written as well) So they are both slow, and not very reliable. If you somehow break the driver / raid table you may lose data in the worse case scenario. Even if the data survived you'll have some hard time recovering it through software.

Not to mention the performance of software RAID5 is VERY SLOW

I tried making a RAID5 on SIL3114 with 4x Hitachi SATA drives, left them overnight to make sure its init-ed completely. I copy 200GB of files through network to the disks. It started off at 76MB/s (limited by network) then after 5 minutes it drop to 300KB/s. Something must have been broken I thought. After that I think, slow write is fine, I only need fast read. I then copy the file to another drive, with just 3G of files the transfer said it will take 45 minutes! I immediately erased the array and go back to independent disks.

It is just not worth the trouble going software RAID5 (especially on a SIL3114)

whilst i agree software RAIDs are stupid, espesually when you've got enough money for 5 drives, i feal i should share some good experiances, under NT, its piss easy to set up (as long as you don't want windows running of the virtual RAID drive, this is understably more difficult to set up, but possible).

Also under BSD, on BSD with a dual xeon neccona's I found the performance to be about 10-20% worse than with my hardware RAID card (which at the time i thought might of been making my instabilities). NT i found to be slightly slower at writes, but faster at reads, go figure, i didn't look at how much RAM it was using as a cache, as it was more an experiment.

Software RAIDs can be done, but their even more easy to trash.

with RAIDs, if you think YOUR more likely to loose data than your HDD, dont bother with a pairty based RAID!

Quote:

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Originally Posted by dangel

With all the posts on how great hardware RAID is compared to onboard stuff - what's a good one to go for? All i'd need is two-channel, maybe four if afordable, and i'd prolly stick with striped.

Recommendations?

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3Ware or Areca...both start at around 200-250ukp. You do get what you pay for though :)

Quote:

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Originally Posted by TheAnimus

whilst i agree software RAIDs are stupid, espesually when you've got enough money for 5 drives, i feal i should share some good experiances, under NT, its piss easy to set up (as long as you don't want windows running of the virtual RAID drive, this is understably more difficult to set up, but possible).

Also under BSD, on BSD with a dual xeon neccona's I found the performance to be about 10-20% worse than with my hardware RAID card (which at the time i thought might of been making my instabilities). NT i found to be slightly slower at writes, but faster at reads, go figure, i didn't look at how much RAM it was using as a cache, as it was more an experiment.

Software RAIDs can be done, but their even more easy to trash.

with RAIDs, if you think YOUR more likely to loose data than your HDD, dont bother with a pairty based RAID!

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You mean the built in striping (raid 0) and striping with parity (raid 5) that NT had in drive manager ? I used to us ethat and never had a problem. Moved onto Win2k and for some reason the second option was gone - or I couldn't get it to work. I ended up going for plain striping of 4 scsi disks (2*2) but as you say you can't do the system drive.

mj