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RAID5 on 3 legs! What leg should I get?


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#61 +LogicalApex

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Posted 11 March 2014 - 16:52

Isn't that response against what you were saying earlier in the thread about 10^14 error rates (in WD Red) for RAID 5 almost certainly leading to a rebuild failure? I was under the same impression you were about rebuild failures until out of curiosity I searched and found the link I posted. Both what I linked and what you linked seem to come to the same conclusion that the probability can't be concluded using that math (my link due to them not finding those failure rates in practice, your link due to the assumptions being incorrect).

It doesn't disagree with it, but I think it offers additional information to the mix. I feel the reliability of RAID 5 on a consumer class HDD of a large size would be very suspect, but it probably won't end up in a death either depending on the RAID controller. Enterprise grade stuff like the LSI controller in my server will handle a rebuild failure a lot smoother than a crappy HiPoint or software RAID in my experience. Since the LSI can restart a rebuild you can recover from a failed read a lot easier.

 

I would say I would be suspect of a large drive RAID 5 array using consumer quality HDDs on a cheap RAID controller.

 

I make heavy use of RAID 5, but I currently keep it on SAS drives due to the increased reliability of the drives overall. Either way, backups are paramount. Without them you still have substantial risk on the table. Especially if you're not using an Enterprise grade controller. As a controller failure can kill the array since a lot of lower end stuff can't cross talk. I moved a RAID 5 array from a LSI 8308ELP to a Dell Perc H710 (LSI based controller, but 4 years or so newer) and the H710 imported the RAID array without any loss and rebuilt the parity to newer standards without loss. This would help in a hardware controller failure situation, but only if you have a quality hardware controller...




#62 +snaphat (Myles Landwehr)

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Posted 11 March 2014 - 17:27

It doesn't disagree with it, but I think it offers additional information to the mix. I feel the reliability of RAID 5 on a consumer class HDD of a large size would be very suspect, but it probably won't end up in a death either depending on the RAID controller. Enterprise grade stuff like the LSI controller in my server will handle a rebuild failure a lot smoother than a crappy HiPoint or software RAID in my experience. Since the LSI can restart a rebuild you can recover from a failed read a lot easier.

 

I would say I would be suspect of a large drive RAID 5 array using consumer quality HDDs on a cheap RAID controller.

 

<snip>

This is pretty much my opinion also. An older brother of mine is doing this with around ~20TB of consumer drive space (so with the lower reliability) (as of last week). I don't know what hardware controller he is using but he definitely isn't doing backups with his setup. I immediately assumed some catastrophic failure would occur at some point and told him so. He apparently doesn't think there will be an issue because all of his smaller hardware raid setups over the years never had an data loss issue.



#63 TPreston

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Posted 11 March 2014 - 17:39

Or you could just get a 20$ enterprise raid controller off ebay (HP P400 or later) and do RAID 6. Cheap drives, Cheap controller but with Double Parity;

 

Unless your restricted sinology or qnap's exorbitant prices for extra bays RAID6 is the way to go.

 



#64 duddit2

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Posted 11 March 2014 - 17:46

I would have a rethink on the storage solution with large drives. RAID5 with this size drivesisn't necessarily the best solution any more. I would look at this site and plug your numbers in, http://www.raid-fail...d5-failure.aspx and see what you get.

 

Other good reads.

http://www.zdnet.com...ing-in-2009/162

http://www.smbitjour...-more-reliable/

 

I agree, RAID 5 and large drives is a recipe for disaster due to the high chance of unreadable blocks on none failed drives happening at the same time as a drive goes bad being very high (more storage available per drive = more chance of unreadable blocks per drive = more chance of an unreadable block on a good drive when one is down).

 

RAID 5 is really in its final stages of life now, and far better options are available.



#65 +LogicalApex

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Posted 12 March 2014 - 04:45

I agree, RAID 5 and large drives is a recipe for disaster due to the high chance of unreadable blocks on none failed drives happening at the same time as a drive goes bad being very high (more storage available per drive = more chance of unreadable blocks per drive = more chance of an unreadable block on a good drive when one is down).

RAID 5 is really in its final stages of life now, and far better options are available.


What are the better options? RAID 6 is very expensive with 2 drives dedicated to parity.

The myriad of software RAID options I see appearing seem very risky. Many take advantage of system RAM as a cache to improve performance as well. Unless you are using Enterprise components (ECC RAM) then you could have corruption occur silently in RAM. As most users tend to not use ECC chips...

I think it is safe to say that there are choices, but better is very situational.

#66 +BudMan

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Posted 12 March 2014 - 19:55

What are the better options? RAID 6 is very expensive with 2 drives dedicated to parity.
 

I think it is safe to say that there are choices, but better is very situational.

 

We are talking the home setup right, storage of "media" library?  Why would home user even need parity at all for such data?  And if they did want to use some parity - why would they include the parity in the array - why not use something like unraid to provide their parity on a disk outside of the storage without stripping.  If that disk is lost you don't loose any data from the array, if a disk in the storage is lost it can be recreated from the parity..  If both the parity and other disks are lost - you only loose the data on the disks, not the whole array.

 

With the speed of modern drives - An array of disks is not needed to provide for more read speed of the data.  The data in a home is not mission critical - why a home user would be spending money on its storage like it is seems money wasted to me..   In my personal opinion your wasting time, effort and money if your running raid 5 or 6 or any other raid that stripes your parity across your array.. It just does not make sense in a home setup for a "media library"..  Now if you have money and that is how you want to spend - more power to you, its your money its your data.

 

But I think there are many "better" options that give the home user more bang for the buck in storage and in the long run are less likely to cause a catastrophic loss of their entire library from one mishap.

 

Drive pooling is much better suited for storage of "media" that can be replaced..  Its easier to maintain, its easier to expand, easier to access and understand nontech user and even if disks fail you only loose the data on those disks and only have to restore the stuff that you lost if you desire.  And with the proper tools the risk of disk failure can be monitored and preventive replacement can be used to minimize loss of data on the drive because it fails.  Since the disk only has to be accessed and even spun up when data is either written or read from it vs every single read/write to the array because of stripping and parity creation.  The disk should see less wear and tear then a disk in say a raid 5 - so in the long run longer time to failure.

 

It is just "copies" of music and video that can be replaced - you just like having it at your finger tips..  Maybe this is just me - but lets say I lost my whole library..  Sure it would suck and all, but I don't even know when I started the rebuild if I would restore it all.  Music sure over time I would rerip my collection - but some of the movies/tv/etc maybe not get put back..  My home movies and pictures would be restored first - and they are easy to restore from backup, disk or optical disks or even just download from the cloud..  Those are "critical" files and being such have backup and DR because they can not be replaced, unlike the copy of the remastered star trek original series.. Which if worse came to worse I could just order another copy from amazon or itunes.

 

Unless the data has to be online 24/7/365 (enterprise data) I just don't see why users would be spending money to try and do that.  When that money could be used to buy more movies/music for one :)
 



#67 OP riahc3

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Posted 12 March 2014 - 21:58

Hello,

To further BudMan's point, with storage pools, you can also make a fake RAID5 so to speak; You "waste" more space than a regular RAID5 but you have the ability to move your RAID5 almost freely under a Windows environment.

That's what really convinced me :) My storage pool will be mostly a mix of RAID5 and RAID1, so to speak.

#68 OP riahc3

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Posted 13 April 2014 - 19:53

Well, another one hit the dust so Im gonna go with a WD30EFRX since I have the 4TB version at work and they seem to be OK.