2 HDD RAID 0 vs. 4 HDD RAID 0+1

bdollar

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Taking cost out of the equation I have a question about speed performance of RAID. Does RAID 0 of 2 HDD outperform RAID 1+0 (or 0+1, not sure if it matters) using 4 HDDs? Same size drives etc. I don't know a ton about this so not sure if since you are backing up it is always going to slow it or as long as you have the same size, speed, etc it is pretty much the same. This is performance for a home system, not server type application.
 

gagaga

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Go with RAID 10 - you won't really notice it being any slower than RAID 0 on a decently fast system.

By the way RAID 10 is 1 then 0 - ie, mirrored disks that are then striped. Good thing is you can lose 1 disk from either pair and not lose any data ...
 

PraxGTI

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RAID 0 is going to be the best performance.

I am running Raid 0+1 (2 Raid 0's in Raid 1) with 4 drives and I am very happy with the performance. It is better than Raid 5, and only (if any) slightly lower than Raid 0.

With 4 500GB drives I end up with ~1 TB of space in 0+1.
 

halcyon

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You could, depending on the data that is important to you, do the RAID 0 to get the best peformance and just do backups to a seperate physical disk(s) on the data that's important. The likihood of losing the RAID 0 array and the backup simultaneously due to disaster is quite slim. I've been lucky with RAID 0, been using it since back in '01 on multiple machines and I've never had a drive fail (I know that's lucky, but its true) and I just do daily backups of the important stuff.

1) I never mind rebuilding the OS since its an opportunity to do a clean install that can be perhaps slicker than the last one. I've never had to to a rebuild due to a RAID 0 failure.

2) A 2 or 3 disk RAID 0 would give you nice performance

3) You NEED to do regular backups anyways regardless of the RAID level you use for issues such as versioning.

That might not be the most popular approach but its worked for me since 2001

 

russki

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Cool. Waste of money vs. bigger waste of money.

But that's right, cost is out of the equation, so whatever TSIMonster said. Minus the good route part.
 

russki

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By the way, I know this is not the forum, but...

The new layout blows chunks and makes it difficult to participate. There.
 

bdollar

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halcyon,

in reference to your #3:

I'm pretty new to this. Can you explain a little. By back ups do you mean a program that does that or actual additional drives? thx and sorry to everyone else if this is lame/obvious.
 

halcyon

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The RAID 0+1 gives you some physical protection against disk failure. Important physical protection, I'm not purporting otherwise. A decent (even free) data backup program can give you "versioning". Let's say you've got your doctural thesis. On Monday you make edits, they get backed up. On Tuesday you make further edits, they get backed up. Wednesday and Thursday are the same...more edits. On Friday you realize that you need Monday's version. You go back to your seperate hard drive and pull Monday's version from the backup. The same thing could happen to the $2K Photoshop project for your impatient client.

I'm oversimplifying this (unless you use Version BackUp, which is indeed this simple).

...bottom line. You need a backup program to do data backups, regardless of whether you're using RAID 1, 5, 0+1, or AID 0.

Whenever doing AID 0 (there's not Redundancy so why call it RAID) its even more critical to backup to a separate hard disk. I'm sure AID 0 arrays do fail, even though not in my experience, so its critical to do data backups often.

Note: I don't recommend putting economical drives (with lower MTBF rates) in AID 0 arrays for seemingly obvious reasons. I'd stick to Enterprise-class drives just for their higher MTBF rates.

You may not have been looking for what I wrote and I don't mean to patronise. Hope it helps.
 

TSIMonster

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If you need redundancy, RAID is the best way to have it. RAID 01 or 10 is a way to get redundancy and a speed boost. It is a GREAT route to go for high availability...

 

bdollar

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I understand what RAID 1 and 0 are but I am not really understanding RAID 1+0 vs RAID 0+1. So stripe then mirror or mirror then stripe but does it really matter? Is one way faster than the other? Can you really set it up either way or is it just two ways to say the same thing? Thanks!
 

maximiza

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Raid 0 is not really raid since there is no fault tolaernce. You loose everything at failure. But it is the fastest with the highest risk. RAID 0+1 is really used for file server junk, very expensive. Raid 5 is better then raid 0+1. I have never heard of a raid 1+0, Maybe they mean raid 10?
 

bdollar

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I think as HDDs continue to fall in price the 0+1 option is getting to be less of an issue on price. If you can get almost the same performance as two mirrored drives but have them backed up that doesn't seem to be a bad thing. As far as RAID 10, I always thought that was just another way to say RAID 0+1 but I never knew if it is all the same thing and people just write it different or if it is really different. Same goes for 1+0. Don't know if it is just the wrong way to write it when you are really talking about 0+1 or if it is really another way to RAID them.
 

bdollar

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Also, why is RAID 5 better than 1+0, just cost or is there some other benefit? I thought 5 was a cheaper (only takes 3 drives), slightly slower option vs 0+1.
 

TeraMedia

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RAID 0+1 vs. RAID 1+0 are different, and the difference has to do with the redundancy level. Think of a byte "AB" being written to RAID 0 (I know - stripes are bigger than a byte...). You get "A" on drive 1 and "B" on drive 2. Now imagine that each drive has a mirror, 1' and 2'. If you lose 1 or 1' (but not both), you still have "A". If you lose 2 or 2' (but not both), you still have "B". So you can lose two drives and still maintain your data, as long as the drives lost are from different stripes.

Now reverse the scenario so that you first mirror, then stripe. So you have "AB" going to one half of the mirror (12) and "AB" going to the other half of the mirror (1'2'). The striping puts "A" on 1 and 1', and "B" on 2 and 2', but if you lose either disk 1 or 2, then mirror 12 is defunct - and your data is only available on mirror 1'2'. So you could lose two disks on either half of the mirror, but if you lose a drive on both sides of the mirror - even for different stripes - your data is toast. Of course, as soon as one disk fails in half of the mirror, that half is defunct so it doesn't really matter if the other goes too, as far as data recoverability is concerned.

Read more about this on wikipedia.

RAID 1+0 (or 0+1 - whichever is the name for what I'm writing about and am too lazy to look up) is pretty good performance wise, and will only take a significant hit for high-rate small-file IO ops due to disk access times. This can be mitigated by using write-back-cache, but don't do that unless you have some battery backup power supply - either for the controller itself or for the entire computer. Otherwise, a power glitch could cause the array to lose coherency.
 

TeraMedia

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RAID 5 can use 4 drives very well - in fact, the more drives you have, the more efficiently your disk storage space will be used because the parity data storage (1 of n) will represent a smaller portion of the overall disk storage space.

RAID 5 with 4 disks is faster for reads than RAID 1+0, because it acts like RAID 0 with 3 disks. RAID 5 can be slower or faster for writes, depending on controller used and configuration.
 

bdollar

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Ok one more question on this. Although I like the scoop on the RAID 5 and after going on line and reading more i can see how 4 drives in RAID 5 would work pretty slick. I still have one more question on 0+1 vs 1+0. I now understand how they work differently as far as protecting data and what kind of failures have what kind of effect based on which one you choose but does anyone know performance? Will 0+1 have a better/worse/same than 1+0?
 

iocedmyself

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RAID 0+1 is a mirror of stripes
For example six 250GB drives used in raid 0 to create two 750GB RAID 0 array's. Then those 750GB arrays are put into RAID 1.

RAID 1
______________________
| |
RAID 0 RAID 0
_____________ _____________
| | | | | |
250GB 250GB 250GB 250GB 250GB 250GB
A1 A2 A3 A1 A2 A3
A4 A5 A6 A4 A5 A6
A7 A8 A9 A7 A8 A9
A10 A11 A12 A10 A11 A12

RAID 10 is a stripe of mirrors
Six 250GB disks in three mirrored pairs then put into a RAID 0 array to achieve 750GB disk.
RAID 0
_______________________________
| | |
RAID 1 RAID 1 RAID 1
_______ _______ _______
| | | | | |
250GB 250GB 250GB 250GB 250GB 250GB
A1 A1 A2 A2 A3 A3
A4 A4 A5 A5 A6 A6
A7 A7 A8 A8 A9 A9
A10 A10 A11 A11 A12 A12

Raid 0+1 will generally have better write performance, where Raid 10 will have better read performance. But even that isn't absolute as it depends on what type of hard drives you're using, the controller and the actual file sizes that would be transfered/accessed.

ULTRA 160/320 SCSI disks have better performance with small files, thus are better suited for web servers, data servers, or even just your OS swap file. SCSI of course has the added benifit of being able to have 16 drives attached to one controller, though there is still the max transfer speed of 160/320 MB/s on the raid controller whether it be a single channel RAID card with 16 disks, or 8 channel card with 2 disks per channel.

Sata drives are better suited for large files, uncompressed photos, Video files, disc images etc. With sata there is the added benifit of 150 MB/s - 300 MB/s theoretical transfer per channel, and since most of us haven't adapted the SATA splitter hubss it's a safe bet you won't have to worry about transfer bottleneck with a single disk per channel.

However now that technology has caught up a bit, RAID 5 is actually the best performance/data security solution. Only drawback being that you need a good raid card to be able to pull off RAID 5 without it having huge system overhead, but still more worth it imo. RAID 5 really doesn't have a disk limit for an array anymore as far as i know, and for example if you have 7 disks in RAID 5, you only lose one disk worth of storage capacity to redundancy data....well that's true whether you have 4 disks or 16.

My media server is set up with 7, 74GB 10k RPM 16MB cache SCSI disks in RAID 5 for storing application data and the like, with 4, 500GB SATA II disks in Raid 10 for video files and disc image back ups. I'll be adding another rack of 74GB SCSI's in the next week or so, to get 900 Gigs of Raid 5 SCSI storage and 1 terabyte of SATA sorage. Sata performance is 50-65 mb/s disk performance over a gigabyte ethernet line, the SCSI performance is equivolent on network, and 90 MB/s or so sustained performance moving files internally.


 

russki

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EXCEPT if you do need the redundancy of the RAID10 caliber, there are better options, like a 5, for example, or 6 if you want improved redundancy. No one sane would really entertain 10 or 01 if it is a real need, and no one without the real need should consider it in the first place.
 

russki

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bdollar, you start doing 5 on cheap (particularly built-in) controllers and you defeat the purpose. They do not perform well. You want a high quality controller for decent RAID 5 (let alone 6) implementation.
 

Hovaucf

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Either do a RAID 0 or RAID 5.

If you do RAID 0 get at least 3 drives, 2 for RAID 0 and 1 for backing up data you would rather not lose.

RAID 5 you will need at least 3 drives and get a decent RAID Controller from Adaptec, 3Ware, or LSI.

Go HERE for a good visual explanation of RAID levels and which will pertain to you.
 

TSIMonster

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See, you are missing some of the points of RAID 10 an 01. For simple redundancy most use RAID 1. Now, lets say you what to add some storage space but keep redundancy... You could buy 2 more cheap drives use RAID 10 or 01. Added storage with retained redundancy. No need to be a smartass, this is a simple discussion, nothing more.

Furthermore, RAID 5 is subject to some of the same pitfalls as 10 or 01. In RAID 5, if more then one drive fails then there is data loss. RAID 10 is better in this aspect because the array can sustain multiple drive losses so long as no mirror loses both its drives.
 

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