RAID 0+1 vs. RAID 5

[millhouse]

EDIT: Fixed the first configuration.
EDIT 2: Fixed the second configuration.

I'm building an AM2 system at the end of July, and I'm getting an Asus 570 chipset mobo with it. It offers 6 SATA ports to play around with on the default controller, as I'm sure many of you know. So the question is this...

What is going to give more performance for the price?

5 drive RAID 0 with a mirror set up in Windows (5 80 GB drives stripped, 1 400 GB mirror)
-Pros
Usually faster than RAID 5
Less CPU intensive
-Cons
More expensive
Not as configurable
-Storage
~400 GB
-Price
~$400

OR

6 drive RAID 5 (6 80 GB drives)
-Pros
More configurable
Cheaper
Can be changed later on
-Cons
Generally Slower
Less overall storage
-Storage
~400 GB
-Price
~$270

[synthetic_fenix]

How are you figuring that you are only going to get 240gb with 6 80Gb hard drives in Raid 5? Raid5 is (Total Amount of drives) - (1 drives) = Total Space. In this case (6 * 80 = 480) - (80) = 400. So in Raid 5 you will have a total of 400Gb of space.

Here are some links of raid levels explained

Raid 0+1 http://www.acnc.com/04_01_0_1.html

Raid 5 http://www.acnc.com/04_01_05.html

And after reading those links, You wouldnt be able to do that Raid 0+1 array like you want, 0+1 is a mirror of stripes, had the same fault tolerance as Raid 5 and with 6*80Gb drives you would only have 240Gb total.

[uOpt]

RAID-5's COU requirements are also overstated by now. If you have a beefy 2006 CPU it's not much of an issue.

The main problem with RAID-5 is that a drive failure has a substancial recovery time and you are the screwed soup chicken if a second drive fails during that period.

[ajrettke]

I think your wasting your time and energy with all those configs. I'd run a RAID 1 with 2 larger disks...MAYBE a 0+1 with 4 disks.

RAID 5 with an onboard controller would be a joke (unless it has onboard XOR controller...it's the fact it has to take the time to send parity calcs to the CPU and then get them back...large latency delay which hurts, not the few CPU cycles eaten up)

The only onboard RAID 5 controllers I've seen (w/ XOR) are on server/workstation boards with U320 connections, never seen sata.

Another option would be to just run a normal disk setup or RAID 0 if you think it's better, and have an incremental backup done at night...if something does go wrong you lose that days data, which for personal use probably isn't a big deal.

[Snugglebear]

A RAID1 set that's unbalanced - i.e. one side of the mirror is faster than the other - will have terrible write performance. There's also no guarantee that the controller will issue read requests to the faster side.

There are RAID5/6 SAS controllers trickling out onto the market now with some good capabilities. The new MegaRAID SAS units, for instance, have full hardware support of RAID5 and work with both SAS and SATA drives. While I'm not sure how many have been integrated onto aftermarket boards yet, I do know that Dell has already released them on their new Dempsey/Woodcrest servers.

[millhouse]

How are you figuring that you are only going to get 240gb with 6 80Gb hard drives in Raid 5? Raid5 is (Total Amount of drives) - (1 drives) = Total Space. In this case (6 * 80 = 480) - (80) = 400. So in Raid 5 you will have a total of 400Gb of space.

Here are some links of raid levels explained

Raid 0+1 http://www.acnc.com/04_01_0_1.html

Raid 5 http://www.acnc.com/04_01_05.html

And after reading those links, You wouldnt be able to do that Raid 0+1 array like you want, 0+1 is a mirror of stripes, had the same fault tolerance as Raid 5 and with 6*80Gb drives you would only have 240Gb total.


I don't think so. If I had six drives in RAID 5, an equivalent of 3 of them are going to be dedicated to parity data. That picture of RAID 5 is deceiving. Take the first parity for example. You have A1, B1, C1, D1, E1, and the 1 parity. The parity needs all of the data from the other 5 drives to complete itself, hence making it just as big. This will make it half stripped and half parity.

Thanks for correcting me on the 0+1 arrary. What I SHOULD have said is that I could create a 5 drive RAID 0 array, and THEN add a mirror through LDM in Windows. So I would have 5 stripped drives and a single mirror (which is not stripped at all).

I should also better explain myself on how I want to use this array (either the above config or RAID 5). This array will be only for a Windows XP install and any PC games with it. ALL media will be thrown on another drive I have (300 GB) because it is not HDD intensive, and I don't want to lose it anyway. It is all backed up on DVD/CD anyway. So the array is just for everyday use, so if one drive goes bad in either config I can fix it. No problems. If two go...well that sucks :) , but again, no loss.

I really appreciate all the input guys, thanks.

[Snugglebear]

I don't think so. If I had six drives in RAID 5, an equivalent of 3 of them are going to be dedicated to parity data. That picture of RAID 5 is deceiving. Take the first parity for example. You have A1, B1, C1, D1, E1, and the 1 parity. The parity needs all of the data from the other 5 drives to complete itself, hence making it just as big. This will make it half stripped and half parity.

This is incorrect - the parity block is not just as big as the data, it only occupies one block on each stripe. Hence the total usable size of the array is as was stated before: sum(all drives) - one drive. If this were not the case everyone would be mirroring their data, as it would be just as space efficient yet faster.

[millhouse]

This is incorrect - the parity block is not just as big as the data, it only occupies one block on each stripe. Hence the total usable size of the array is as was stated before: sum(all drives) - one drive. If this were not the case everyone would be mirroring their data, as it would be just as space efficient yet faster.

How can the parity not be as big as all the stripes put together? :confused:

[ajrettke]

simple.....
6 disks, A, B, C etc
drive A contains the parity information for the first stripe. (so drives BCDEF hold data, drive A holds the parity calc, if one of BCDEF goes down (let's just say C died) information from BDEF would be read and compared to A and the missing value C would be found. So each write uses 5 of the 6 disks for data in this situation...and one drive is consumed by parity aka overhead.
the formula for RAID 5 is correct.

the next stripe, drive B will contrain the parity info...and etc. With this system, if you lose a drive you can still get the information. The reason everyone doesn't do this is for very fast data accessing and writing you need a controller which calculates the parity bit for every write and every read when a drive is down, the controller also has to know the striping order and waht not. These controllers cost a lot to make, which is why RAID 5 isn't used by us desktoppers usualy (200 for a controller on a 6k server isn't that big of a deal).

[millhouse]

simple.....
6 disks, A, B, C etc
drive A contains the parity information for the first stripe. (so drives BCDEF hold data, drive A holds the parity calc, if one of BCDEF goes down (let's just say C died) information from BDEF would be read and compared to A and the missing value C would be found. So each write uses 5 of the 6 disks for data in this situation...and one drive is consumed by parity aka overhead.
the formula for RAID 5 is correct.

the next stripe, drive B will contrain the parity info...and etc. With this system, if you lose a drive you can still get the information. The reason everyone doesn't do this is for very fast data accessing and writing you need a controller which calculates the parity bit for every write and every read when a drive is down, the controller also has to know the striping order and waht not. These controllers cost a lot to make, which is why RAID 5 isn't used by us desktoppers usualy (200 for a controller on a 6k server isn't that big of a deal).

Thank you, now it makes sense! Sorry for the confusion. So what do you all think would be the best of these two possible solutions (other suggestions welcome too)? I've been reading around on benchmarks, and RAID 5 is usually a bit behind RAID 0 in most tests, especially write. However, an extra drive may make up for that difference, and I'd get the benefit of an easier swap if one goes bad and a cheaper cost.

[pik4chu]

RAID 0 is for fans of faster access/write on a personal computer, it has no place in an office environment
RAIS 1 is for a nice solid redundancy, generally used on a server for the OS/apps
RAID 5's use is mainly for redundant data storage as it gives good read/access times and has little use outside the office place, aside from it being a good way to combine drivs into one big one and eliminating the need to do stupid things with windows like dynamic disks

[Mobious]

Is anyone but me gunna vouch for RAID 10 (striped then each stripe is mirrored)? This is my personal favorite: same awesome performance as 0+1 (http://www.pcguide.com/ref/hdd/perf/raid/levels/comp.htm, notice that its the same if not better than RAID 0 but just a little slower and the writes), but you can have one drive from each stripe go down and you'll be golden (just not both of each stripe).

[pik4chu]

Is anyone but me gunna vouch for RAID 10 (striped then each stripe is mirrored)? This is my personal favorite: same awesome performance as 0+1 (http://www.pcguide.com/ref/hdd/perf/raid/levels/comp.htm, notice that its the same if not better than RAID 0 but just a little slower and the writes), but you can have one drive from each stripe go down and you'll be golden (just not both of each stripe).
Its certainly another choice but it wont have that good of performance due to the respective limitations of RAID 0 and 1. Also when using 4 drives you get more space going RAID5, which is why I wouldn't recommend it.

[ajrettke]

The first setup would be worse in terms of performance than just 2 disks in RAID 1....here's why:
The benefit of RAID 0 is high bandwidth...and with a single disk as the mirror your only as fast as your weakest link, thus the single disk....and with RAID 0 you have increased latency compared to a single disk, so you see you'll get worse than just having 2 disks in RAID 0.

I would either:
get 4 disks and run RAID 10/0+1 whatever your controller does
get 3 disks run RAID 0 on 2 and do a backup at night onto the 3rd
get 2 disks run RAID 1 or just run em solo and backup at night.

Raid 5 on this controller is not a good idea, your performance will suck.

[millhouse]

The first setup would be worse in terms of performance than just 2 disks in RAID 1....here's why:
The benefit of RAID 0 is high bandwidth...and with a single disk as the mirror your only as fast as your weakest link, thus the single disk....and with RAID 0 you have increased latency compared to a single disk, so you see you'll get worse than just having 2 disks in RAID 0.

I would either:
get 4 disks and run RAID 10/0+1 whatever your controller does
get 3 disks run RAID 0 on 2 and do a backup at night onto the 3rd
get 2 disks run RAID 1 or just run em solo and backup at night.

Raid 5 on this controller is not a good idea, your performance will suck.

I see what your saying about the mirror, good point. I've decided to go with RAID 5 though. I've seen many benchmarks that contrast with what you are saying about RAID 5. I'll try RAID 5 first, and if it does suck I'll switch to something else. Heck, I might even try a few different configurations just to see how they stack up against each other, and of course report my findings here. :D

[uOpt]

Is anyone but me gunna vouch for RAID 10 (striped then each stripe is mirrored)? This is my personal favorite: same awesome performance as 0+1 (http://www.pcguide.com/ref/hdd/perf/raid/levels/comp.htm, notice that its the same if not better than RAID 0 but just a little slower and the writes), but you can have one drive from each stripe go down and you'll be golden (just not both of each stripe).

It's nice but it doesn't have that much advantage over raid-5 anymore, even in cheap environments. On the other hand it wastes space if you have many drives and it is hard to grow.

[ajrettke]

well if you find that your speeds aren't acceptable in RAID 5 with the onboard controller you can always add a PCI/e/x (not sure what your mobo has) which will help you a lot in terms of performance.

Best of luck with your setup :)