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  Is RAID 6 better than RAID 10 ? 
 
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binar May 17, 2011, 11:30pm EDT Reply - Quote - Report Abuse
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Fellow Forum Members,
I have read the RAID sticky and it seems to be missing a good comparison between RAID 6 and RAID 10. I need to know what to use with my new Areca 1880ix 24 RAID controller card which is connected to 24 SATA 1TB hard drives. Below is the RAID 6 description found in the sticky:

RAID-6 Striping with Double Parity 4 disk minimum plus a proprietary RAID controller:
RAID-6 is the exact same thing as RAID-5, but it offers double the parity of RAID-5 so that way you can sustain a two disk failure and still retain your data.

Is RAID 6 a better than RAID 10? How many drive failures can RAID 10 have? I was told that RAID t0 backs up the data on a 1 to 1 hard drive ratio. Therefore, for my example of 24 SATA 1TB hard drives, 12 hard drives will be allocated to data and 12 to backup data. What is the RAID 6 ratio? Is RAID 10 a more dependable option when compared to RAID 6 since half of it is dedicated to backup? I'm seeking to choose the correct RAID option. Because the bottom line is I only want to migrate my data only one time and never mess with it again or worry about backups. Any advice will be greatly apppreciated. Thank you.


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G. G. May 18, 2011, 10:28pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
If you are looking for data protection then go with Raid-6. Yes, Raid-6 can take a two disk hit failure and Raid-10 can only take a single drive hit failure.


Raid-6 creates two parity with each data block and spread it across all the drives and shifts it across the drive set. This method is more algorithm intensive than 10 (striped and mirror).

Raid-10, data is striped across a set number of drives and then it is mirror across to a different set of equal number of drives. So in your case with 24 drives... yes... half will be data and the other half will become the mirror of that data. One set will be the primary and the other is the backup... But no matter how many drives you have, if you loose 1 drive from one set, that set is toast but your data will be running on the mirror set. Once you replace the bad drive in the set that had the hit, that whole set get rebuilt from the mirror. But, during the time that you have a bad drive in one set, you are in a compromised condition in that until you get that drive replace and the set rebuilt, if you so happened to loose a drive in the backup mirror, your whole data is a gonner. Bottomline is that if you loose a drive in either set, that whole set has to be rebuilt before you are back to redundant.

Back to Raid-6, as mentioned, the data and two parity gets laid down across the drive set in a rotational manner... when you have a drive failure, your drive set continues to operate on all its drives less the bad one.... once the bad drive is replace, that drive gets rebuilt using the parity data that is stored on the other drives that belongs to that drive. Since there are two parity data being created, you are able to take a two drive hit....and both drives will be rebuilt by the parity data that is stored on the working drives once the bad drives is replaced. But if you take a third drive hit..... um... the whole kabultoos... is down the drain..

If you got a decent hardware raid .... I'd go for raid-6.


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john albrich May 19, 2011, 01:30am EDT Reply - Quote - Report Abuse
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Edited: May 19, 2011, 01:46am EDT

 
>> Re: Is RAID 6 better than RAID 10 ?

I agree with G.G.

and for backup use a backup program with compression and scheduling capabilities (or alternatively use batch files and Windows scheduling with a backup program that has command-line options like Macrium Reflect...which is what I do). Between the redundant parity protection of RAID6 and a robust backup protocol you'll be in good shape.

In addition, locate your backup drives in their own power subsystem and protections and you improve your resistance to a single-point catastrophic failure taking out your main and backup drives. You could even distribute the backups amongst other systems in your network.


Here's an example using MacriumReflectFreeEdition and a .bat file using Windows scheduler to create a daily backup of the system drive. Note that MRFE allows you to create .xml backup macro files that control how the backup occurs (e.g. with or without compression, "intelligent" backup or full content, where the backup is to be stored, etc ). These .xml files are created AUTOMATICALLY for you by MRFE when you perform the first backup and you can re-use them from then on, so you do NOT need to know how to write any code to make them.

For example, you might setup Windows scheduler to run this .bat file at 2AM every morning.
echo off
REM Daily Drive C backup batch file using Macrium Reflect Free Edition
REM Ver 201008070443
REM Dependencies
REM T:\DriveC_DailyBackup_MR.xml backup definition file created under MRFE
REM MacriumReflectFreeEdition (verified under Ver. 4.2.2952)

REM delete old dailiy backup image file to make room for new daily image
del T:\DriveC_DailyBackup_MR\*.mrimg /Q

REM temporarily set execution path to include Macrium
path = %path%;C:\Program Files\Downloaded_apps\MacriumBackup

REM The specified .xml file is an "intelligent", "medium compression" backup ("intelligent"=no pagefile/hiberfile)
REM -e = execute the .xml file, -w = if MR busy then wait until available
reflect.exe -e -w "T:\DriveC_DailyBackup_MR.xml"


edit to add:
And, you can create weekly and monthly .bat files that save the appropriate files on the obviously weekly and monthly basis, and clear out older copies once a time threshold has passed. For example, you might only want to keep the last 4 weekly backups (for a 1 month recovery capability with weekly granularity), and only keep the last 6 monthly backups with monthly granularity, and so on. And you might want to make sure a given set of backups (e.g. the monthly set) is located or copied to a location completely off-site. Of course how deep and granular you make it depends on just how critical your data and programs are and your disaster planning and recovery protocols.

binar May 19, 2011, 01:17pm EDT Reply - Quote - Report Abuse
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Edited: May 19, 2011, 01:20pm EDT

 
>> Re: Is RAID 6 better than RAID 10 ?
G.G. and John,
Thanks for your posts. I'm glad I created this thread because I was pretty close to going the RAID 10 route. My goal is total data protection. I do not want to ever in the near future be in a position where I find myself rebuilding my RAID array from scratch a second time. This would be a total pain in the rear.

G.G. the way you explain RAID 6 has convinced me it's the way to go. I have 24 1TB hard drives but in reading through my Areca Controller user manual I learned this card also supports hot swop drives. If a drive falis, without any human intervention, this controller card will automatically rebuild the failed drive data to a hot swop drive. I am currently waiting for two additional 1TB Hard Drives and a SFF-8088 to SATA Fan Out cable. My plan is to assign two hot swop drives using the external 8088 port my Areca card has in the rear. This way I don't sacrifice any of my 24 drives as hot swop drives. I am looping the cable back into the case where my two hot swop drives are located.

Lastly, for 24 drives RAID 10 uses 12 for data and 12 for backup. What about RAID 6? Based on 24 drives, how much of the 24 TB of space will be available for data storage and how much for backup? I would appreciate hearing back from anyone with an answer to this question. THanks.

G. G. May 19, 2011, 02:30pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
binar,


in regards to available/usable space in your example of 24TB hdd setup.... without going into the nittygritty because it depends on a whole lota factors like, size, drive type, drive brand, drive specs, controller's spec, and so on..... a good rule of thumb and ball park.... use the 75~70% gauge being on the conservative side. Without knowing the actual details of the hardware/firmware of the setup .... for a 24TB at 1TB size each... this would come out to be 21.998TB of available space according to my resource.


now as for "hot swop".... lol is this Chinglish????

There are two terms that you need to be aware, they are Hot Swap and Hot Spare....

Hot Swap - means that the controller can handle an event where a drive bites the dust, you can pull the drive and then turn around and insert a new drive all the while with the system and OS fully up and running. So lets say in your setup... a drive pewukes... you get a notification that a drive has failed... you have a spare drive lying around... you go up to your setup and pull the bad drive, insert the replacement drive, and the controller should launch the rebuild process all the while as you return to your Sally does Dallas movie and burning movie iso...

Hot Spare - means that you have a spare drive as part of the configuration set and all it is there for is to sit there waiting for one of the other drive to fail. It is in standby mode. When one of the other drive actually fail, the controller will bring the "Hot Spare" into the group and will start the rebuild process to this drive to make the set whole again. When you go to replace the bad drive, depending on the controller or configuration, the new drive could become the new "Hot Spare" or get copy paste from the original Hot Spare, in which case the original Hot Spare becomes from being part of the group back to being the Hot Spare again.

Now depending on the controller card when it comes to Hot Swap or Hot Spare, it may have one or the other...... or both.... If you dont have Hot Swap, then you will have to shutdown the raid set, i.e. make it unavailable to the OS or shutdown the system in order to replace the bad drive. If you pull the bad drive and even inserting a new drive from the drive set and you DONT have Hot Swap..... you will have the possibility of causing issue with the system like hang, system reset, crash, and so forth... The controller has to have hardware components to be able to handle the bus reset as the drive is pulled and reinserted so as this will not cause electrical issues on the system.

hopefully you are not confused by my explainations

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binar May 19, 2011, 10:19pm EDT Reply - Quote - Report Abuse
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Edited: May 19, 2011, 10:22pm EDT

 
>> Re: Is RAID 6 better than RAID 10 ?
G.G.
Thanks for your excellent overview you provided regarding Hot Swap and Hot Spare drives. I know for a fact my Areca card has the Hot Spare, Not sure about the other.

Moreover, I have to admit the math does not add up for RAID 6. You say that for my 24TB example close to 22TB is available for storing data which means that 2TB is dedicated for actually backing up the data. In contrast, RAID 10 is using 12TB for data and 12TB dedicated for data backup. This math makes sense.

The only way I can rationalize how RAID 6 is able to backup 22 TB of data into 2TB of backup space has to be by using a special form of compression technology. If this is the case, I have to say that the compression algorithm RAID 6 is using to backup 22TB of data into 2TB of backup space is something I find amazing. How is so much data fitting to such a small amount of space?

RAID 6 ioffers a lot more space for storing data compared to RAID 10. It simply sounds too good tbe true. Is RAID 6 performing a partial backup of data that somehow alternates? How does it rebuild the data for any failed hard drive if the size of the backup is so small to begin with. If anyone can explain how RAID 6 performs this magic trick please let me know. Thanks.





G. G. May 19, 2011, 11:07pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
binar,

here is a raid calculator fo you to give a whirl

http://www.raid-calculator.com/Default.aspx


want to know how many drives you need for a given amount of storage needed to a given raid type ? check this out

http://www.dnfstorage.com/resources.asp/section/Reading~Room/c...Calculator


this one gives you some formulas when it is calculating parity..... if you are into this type of thing (formulas that is)

http://en.wikipedia.org/wiki/Standard_RAID_levels


Technical Brief on raid 6 by 3ware

http://www.3ware.com/products/pdf/raid_6_techbrief_112906.pdf


You'll love this one if you arent buzzing just yet... if not... this one will explode your brain

http://www.kernel.org/pub/linux/kernel/people/hpa/raid6.pdf (Mathematics of Raid-6)


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binar May 21, 2011, 08:57pm EDT Reply - Quote - Report Abuse
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Edited: May 21, 2011, 08:58pm EDT

 
>> Re: Is RAID 6 better than RAID 10 ?
G.G.
Thanks for the excellent links. I have looked at all of them and have to say that RAID is a subject that goes very deep in complexity. THe coolest link is the calculator. I tried it out and got results close to what you got.

I have researched RAID technology enough and my decision is that I'm going with RAID 6. Below is a list of some of the positives and negatives I have learned about RAID 6:

1. A negative is it takes longer to bootup compared to RAID 10. I read it is because it's got to go through a two parity check. If it's an extra 2 minutes of bootup time I can live with that.

2. A positive for RAID 6 is that it's a better choice when using Desktop Hard Drive as opposed to Enterprise Business level Hard drives. Desktop hard drives have a higher chance of failing and RAID 6 is designed to cope with failed drives more effectively. Since my RAID 6 is going to be made up of 24 1TB Desktop hard drives, I expect some drive failures in the fuutre. I elected not to go with Enterprise Level Hard Drives because they are a lot more expensive.

3. A negative for RAID 6 is that it has a much longer hard drive failure recovery time as compared to RAID 10. I was told that RAID 6 could take as long as 12 hours to recover from a disc drive failure. Raid 10 is much faster than 12 hours.

4. A negative for RAID 6 is slower Writer times. Read times I was told were the same between RAID 6 and RAID 10.

5. A huge positive for RAID 6 is the Data Storage Space to Backup Space ratio it provides. From what I figure,roughly 80% goes to Data Storage Space and 20% goes to backup space. In contrast, RAID 10 has a 50% ratio where half of the total capacity goes to Storage Space and the other half goes to Back Space. How RAID 6 performs this magic is something that I cant' understand.

6. A negative I was told is how RAID 6 has the potential of losing your entire data if during a 12 hour long hard drive recovery phase an additional hard drive fails.



I would appreciate it a lot if any other forum members out there could contribute any additional positive and/or negatives relating to RAID 6 compared to RAID 10. Thanks to all for their post.



G. G. May 21, 2011, 10:29pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
binar said:
G.G.
Thanks for the excellent links. I have looked at all of them and have to say that RAID is a subject that goes very deep in complexity. THe coolest link is the calculator. I tried it out and got results close to what you got.

I have researched RAID technology enough and ...................

1. A negative is it takes longer to bootup compared to RAID 10. I read it is because it's got to go through a two parity check. If it's an extra 2 minutes of bootup time I can live with that.


4. A negative for RAID 6 is slower Writer times. Read times I was told were the same between RAID 6 and RAID 10.


6. A negative I was told is how RAID 6 has the potential of losing your entire data if during a 12 hour long hard drive recovery phase an additional hard drive fails.





In regards to boot time.... It is not going to take any longer.. During boot, the system is reading. So the system is reading the Data blocks. The involvement of the parity data is during the write operation of Data blocks. The controller writes the Data blocks and then it creates two Parity data (backup info of the data blocks)... But when reading the data, the controller should only be reading the data blocks... So, is the system is just reading, the total time for a boot up shouldnt be any longer.

Write times.... technically, the write times of a raid-5 is a tad slower than 10... raid-6 write times are identical to raid-5. Thats pretty amazing especially when raid-6 has to create two parity data for each write operation.

Losing the whole array during rebuild.... well..... in a raid-5, if you loose a drive, replace the drive, and the array initiates a rebuild.... it is true that if you loose another drive during this rebuild process... you will be up the creek without a paddle. Array goes pooof... BUT, with raid-6.... you loose the first drive, replace the drive, the array initiates a rebuild.... if you so by chance loose a second drive during the rebuild....ummm dont panic... the array is still good. because in a raid-6, you are able to loose two drive and still be ok.... it's the loss of the third drive that will get you. So bottom line with raid-6 is that you dont wait till you loose 2 drives before you decide to start replacing drives..


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Allan Smith Apr 07, 2013, 01:06pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
I know this is belated, but I had to comment.

Excellent reading. I recently had 2 drive fail during a power outage, home use. I have been questioning how to avoid this ever since.

Thank you, very much

AWS

Thomas Mitchell Apr 17, 2013, 02:52am EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
I hate power outages. They kill more hardware than about anything, even lightning.

Let me go back to that example of 24x1TB drives, RAID 6 or RAID 10. It was mentioned that RAID 10 can only lose one drive without failing, whereas RAID 6 can lose two without failing. If this were politics, I would let that slide as party bias. However, if you want the statement to be factual, if not a bit redundant, what it should state is that a RAID 6 can lose as many as two, but no more than two, drives without failing, The RAID 10 can lose as few as one drive, or as many as 12 drives, without failing.

If you play the odds, you are not very likely to be lucky enough to lose 12 drives before failing but, you would likely get at least two, and possibly more. However, a guaranteed two sounds a whole lot better than *probably* more than one.

G. G. Apr 26, 2013, 09:34pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
Allan Smith said:
I know this is belated, but I had to comment.

Excellent reading. I recently had 2 drive fail during a power outage, home use. I have been questioning how to avoid this ever since.

Thank you, very much

AWS


Allan,

your welcome and thank you for the comment. As for your failed drive during a power outage..... The best way to protect your drives or any of the other components for that matter... is to have your system on a reputable UPS system say like a APC. Some folks say that a surge protector is good enough.... Ummmm not always. When it comes to a single surge/power blip.... it may be ok... but when it comes to multiple outages within a short period of time and especially ones consecutives one after the other, which is the worst.... your components is at high risk. A UPS system, not only do you have a surge protection in place, but a battery back up as well between you (your pc) and the unstable power source. If the power surge is so bad enough, the UPS system will give up its life before for your PC.

If you still want to use a surge only protection..... do NOT go with the cheapest one even though your wallet demands it.... Also, make sure that your bios settings is set to stay off and not reboot. You dont want for the system to start rebooting and all of the sudden loose power again during the middle of the boot.

Oh... and remember... components can get blowned out even when they are powered off. lol.


Thomas,

Im sorry but what you just said really doesnt change anything. Your saying the same thing but in a different twist. Kinda like some saying "potato" and another saying "po-ta-to" or the idea of a glass half empty or half full..... Its all the same. but then again, everyone does have the right look at it differently.



Raid 0 : loose 1 drive = toast
Raid 10 : loose 1 drive = degraded : loose another drive = depends ( 2nd drive : if from the fail set = degraded : if from working set = toast )
Raid 5 : loose 1 drive = degraded : loose another one = toast
Raid 6 : loose 1 drive = degraded : loose another drive = degraded : loose 3rd = toast

There you go.... another way to look at it.... all still mean the same thing as originally discussed.

:P

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john albrich Apr 26, 2013, 09:39pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
G. G. said:
...The best way to protect your drives or any of the other components for that matter... is to have your system on a reputable UPS system say like a APC....

We have a decent discussion on UPS at this HWA thread:
http://www.hardwareanalysis.com/content/topic/77881/#593219

Johannes Felten May 05, 2013, 01:31pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
Hi guys,

I'm also in the position right now where I have to decide how to configure my new 8 bay QNAP. I have 8 3TB red discs and I was also thinking about what the ideal setup would be for that. The conclusion I draw from all that has been said above is that RAID 6 is apparently the safer solution simply because of one main factor: Raid 6 will endure the loss off 2 disc failures anywhere across the setup whereas with Raid 10 it greatly depends on where that second failure occurs. Granting that RAID 10 may survive even with more than 2 drive failures, they would have to be specific ones. If the wrong two drives fail you will end up with a total loss of data. In any case, I assume that once the first drive fails one would replace that asap, so the fact that RAID 10 may theoretically endure multiple disc failures isn't really a benefit because you won't wait for additional failures.
I don't mind a longer redistribution of data in case of a disc failure, my primary concern is surviving it altogether.

Regarding hot spares, I was told that if you use RAID 6 a hot spare is overkill, and somewhere I read that in any case swapping a new disc is preferable to a hot spare because apparently with a hot spare some of the initial boot up procedure, or whatever, is omitted and therefore less advisable (???)

Any additional thoughts on this?


Thomas Mitchell May 05, 2013, 01:52pm EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
G.G., If the OP had asked about a scenario like you described I would agree with you, there is little difference. Using only four drives, a "possible two" is statistically close to being "fat chance of more than one."

However, the OP was talking about 24 drives. From a mathematical standpoint, it makes a lot of difference. It makes a difference in how much capacity you have to give up, as well as a difference in the POTENTIAL for surviving the loss of multiple drives. Again, from a practical standpoint, if redundancy is paramount, and you want the closest thing to a guarantee that you can have, a definite two beats a potential 2-12.

If one is going to hypothesize, one should do so using the parameters of the OP's query. Otherwise, why bother?

scott eaton May 20, 2013, 10:36am EDT Reply - Quote - Report Abuse
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>> Re: Is RAID 6 better than RAID 10 ?
A rather biased and not very accurate description of the advantage of RAID 6 of 10.

RAID 10 has one very distinct advantage over RAID 6 (or any other parity based RAID topography), and yet it's omission is the stuff of legend and near hysterical denial.

Quite simply, RAID 10 can take a hard controller fault while RAID 5/6 can't. That is, unless you've got redundant controllers *AND* the non faulting controller is smart enough to know the other controller is faulty, which is frequently not the case. The faulting controller continues to write garbage, and once that parity degradation > two drives you are screwed.

In my 15 years of corporate data center experience statistically I find the odds of controller failure > the odds of two drives failing. I bigger problem is most of the time multiple drives are detected as being faulty the problem is often *not* with the drives but with the controller. Yet we continue to blame multiple drives failing as an issue with the HD's themselves.

RAID 10 constitutes easy space calculation and linear performance plots. RAID 6 requires a Ouiji board because no hardware vendor implements it the same way, and you are not allowed to even discuss the option of controller failures because we all know in the fantasy world of mass storage vendors it never happens. In my world of reality controller faults, even those corrected by firmware updates exceeds the chance of multiple drive failure.

Last, if anybody wants to put identical RAID 6 and RAID 10 based SANs in a room, and then remove the AC unit, I'll happily put any amount of money on the RAID 10 unit staying up longer at higher temps before corrupting LUNs.


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