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Pancakes

RAID5 and rebuild fails

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Pancakes

I heard you guys talking about RAID 5 on the podcast, assuming you have large drives, are you not scared of another drive failing on the rebuild and causing the entire array failing? As you probably know, there is a fairly high chance of another failure on reading 2TB+ off a parity drive

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schoondoggy

It is a concern. It is one reason why I use a real RAID controller when I decide to do RAID 5. I think rebuild times are OK on 2TB drives in a four drive set. The bigger the set, the higher risk of loss. RAID is not back up. Everything that is on my RAID 5 is backed up elsewhere. I have to think the 4TB drives will cause me to jump to a RAID 10 or sets of RAID 1. 

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Pancakes

But then why not just have the drives in a pool and use a scanner or something to actively monitor the SMART/Sectors? In a home server environment its pretty unlikely a drive will just drop dead. And like you said, its backup up anyway.

 

If you just have them in a pool, you can tell when its failing and start moving the data off the failing drive, so you are not "using up" the other drives and risking a failure.

Edited by Pancakes

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jmwills

Most everyone is using RAID for their data vs a pool because of speed.  The RAID Controllers have settings to advise me of a failing drive so I don't really see the need to add overhead just to get that function from a pool.

 

Just my thoughts and opinion.  YMMV

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Joe_Miner

But then why not just have the drives in a pool and use a scanner or something to actively monitor the SMART/Sectors? In a home server environment its pretty unlikely a drive will just drop dead. And like you said, its backup up anyway.

 

If you just have them in a pool, you can tell when its failing and start moving the data off the failing drive, so you are not "using up" the other drives and risking a failure.

 

You've pretty much described, IMHO, a big benefit of Stablebit DrivePool and Scanner -- both of which I use in my WHS-2011.  There's a lot of info Links in the Hardware Links Page on Drive Extender Replacements, RAID, RAID References, Drives & Drive Performance.  For sure you'd want to listen to HSS #216 & #219 as well as BYOB #120

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ikon

As schoondoggy said, RAID is not a backup -- it's resilience. As long as you have good backup available, a 2nd drive failing in a RAID Array is basically a non-issue. If it happens, replace both drives, create a new array, and restore all the data from one of the, hopefully, numerous backups.

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pcdoc

I heard you guys talking about RAID 5 on the podcast, assuming you have large drives, are you not scared of another drive failing on the rebuild and causing the entire array failing? As you probably know, there is a fairly high chance of another failure on reading 2TB+ off a parity drive

 

In short no.  I have lost a drive a couple of times and unless you let it go for days, weeks, or ???, you should be back up in 5-8 hours fully rebuilt.  As other said, RAID like any other solution, is not a backup however it is far more reliable than single drives or most other solutions.  You can decided which raid level works for you 5, 6, 10, but for the past many years I have run it, I would not go anywhere else.  That said, I am only talking about using a controller not the motherboard.  As jmwills pointed out, speed is by product of having a painless way of keeping my time up and my pain threshold down.  This of course is my two cents.

 

 

http://thedocsworld.net/painless-drive-failure-recovery-the-way-it-should-be/

 

http://thedocsworld.net/category/raid/

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timekills

I've gone back and forth between RAID 6 and RAID 5 with a hot-swap. RAID 6 answers the question about losing a second drive, but with the increased overhead and of course the array is still slower once you lose the one drive. Not to mention if you run into an issue where more than one drive fails within the time it would take to rebuild your array it means you've got either a bad bunch of drives, a bard RAID card, bad power, or just bad something else that needs to be fixed.

 

As mentioned above, I use RAID to give me cheap and fast access to large file movement. RAID 5 is simply the fastest way for me to combine multiple drives in relatively simple fashion and not worry about one bad drive killing everything. 

 

One of these days I might try one of the various drive extender replacements. Those of us used to RAID chuckle when we hear someone say RAID is "too complicated" to use, but my aversion to the drive extender replacements is not significantly different. I have no reason to be averse to them, I'm just not familiar with them.

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pcdoc

I have used them and they are OK but it certainly does not perform as a RAID 5 personally, I also think it is easier.  The drive labeling philosophy is a bit different with extenders and if configured right, a raid card rebuilds much faster and easier than the extenders.

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