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raid5 setup best practices - recommended controller advice

Posted on 2011-10-15
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Last Modified: 2012-05-12
I am looking to get a large RAID 5 or 6 volume around 14TB setup.  It will serve as an archive server images.  I am trying to do this on a budget so i don't just want to throw money at the solution, but at the same time i want something i can count on.  Reliability is my top priority with cost coming in a close second.

Does anyone have a recommendation as far what drives i can get away with?  are basic 2TB drives probably ok in a RAID6 because of the global hot spare?  i can purchase those for about $70 each on newegg.com  Will using low cost drives instead of enterprise drives put me at a high risk of having problems?

What entry level controller card will get me in the door on this?  I'm looking at the adaptec 5805 or 51245.  Will either of those do a good job?  is the 51245 overkill?  I plan on using a SFF-8087 to SATA breakout cable on these, is that something that might be a problem?  Should I use a server case with a back plane instead?  Is there anything I may be overlooking from what i have said.  All i am really considering critical to what i'm doing is what i've mentioned.  Should it matter, I plan on managing this from a Win7 Pro box.

5805 - http://www.adaptec.com/en-us/products/controllers/hardware/sas/performance/sas-5805/

51245 - http://www.newegg.com/Product/Product.aspx?Item=N82E16816103213
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Question by:AdvNetSol
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Author Comment

by:AdvNetSol
ID: 36973573
I should add that downtime isn't a concern.  This storage system will never be used except to dump data manually from time to time.  Theoretically, the device could be powered off for almost a month without causing any problems at all.  I just need to make sure data is never corrupted or completely lost.
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Accepted Solution

by:
David earned 1500 total points
ID: 36973592
your options are limited with those cheesy desktop class drives.  first dual redundancy is an absolute.  with a raid 5 then it is a statistical certainty due  to ECC error rate alone that a rebuild will fail due to the limited number of ECC bits.  

lose a disk & you will lose SOME data.  so R6 is necessary for that alone.

only practical opption is do this with Solaris and a RAIDZ2 volume. this works with desktop disks.  you can also add some SSDs for caching into the volume to help with performance.  forget using a RAID controller.  anything that handles RAID6 won't work with deskto disks due to firmware requirements..  
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Author Comment

by:AdvNetSol
ID: 36973610
It sounds like i need to use enterprise SATA drives then.  If desktop class are not reliable or something that gives me high probability of running smoothly for 3 years then i don't want to mess with it.  Why do you say to forget using a RAID controller?  i would consider that a must.
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Assisted Solution

by:David
David earned 1500 total points
ID: 36973638
zfs is SOFTWARE based RAID. much smarter then any hardware based, until you get  into EMC, netapp, etc..

RAIDZ2 is like RAID6++ It adds extra redundany and protects against data loss, even if you don't jhave a ups.  HOT Snapshot, data compression & deduplication. add new disks live for extra redundancy or expand. you can even use disks of different sizes. I was recently at a cloud providors site. they put 250 TB per server and performance is fine.  since zfs is ppart of the kernel it is  much more efficient  then raid controllers. plus system RAM is used as read cache so you can  have cached reads in nanoseconds instead of milliseconds..
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Assisted Solution

by:David
David earned 1500 total points
ID: 36973663
but use enterprise disks, as many as budfet allows. benefits in other areas such as internal error correction & tolerance for vibration..   you can easily lose more than 50 percent of throughput due to crappy enclosures and shakinng disks.  I recently saw a site that went from sustained 50mb/ per disk to under 20mb/sec avg... after they relocated to new site.  disks were at top of inexpensive racks that were a bit wobbley.  vs being racked at bottom of high  guage metal racks bolted to floor.  that was the only change.
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Assisted Solution

by:andyalder
andyalder earned 500 total points
ID: 36973836
Of course if you use enterprise SAS or SATA which have time limited error recovery or whatever the manufacture wants to call it you can use a hardware RAID controller with whatever OS you choose, it's just disks designed for desktop use that don't work well with hardware controllers since when they go into multiple retries the controller kicks them out of the array.
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by:David
David earned 1500 total points
ID: 36974014
right ... to be clear.. programmable retry timers, or none-programmable recovery that guarantees the disk aborts a read after a few seconds rather than going on for well over 30 second PER BLOCK is a standard feature in enterprise disks.  most controllers require this as they will think a disk died if it takes more than 7 - 10 seconds to returm.

so desktop disks doom your data if you have a few sequential bad blocks on more than 1  disk. with trillions of blocks total, you will have this.

windows software raid & solaris zfs (among others) will wait for a desktop class disk.  downside is that those disks aren't being told that the data it needs elsewhere is available .. so IO hangs for 10+ seconds.  you've no doubt seen a pc hang that long with mouse working but applications freezing.  this is usually the issue.

so enterprise drives limit hangs to only a few seconds max.
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Author Comment

by:AdvNetSol
ID: 36974259
that's very good to know.  Based upon what you are saying, desktop class disks actually will cause fewer problems if i used the RAID built into windows?  

What does RAIDZ2 cost for a setup like this (ballpark)?  Is that something you know off hand?
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Assisted Solution

by:David
David earned 1500 total points
ID: 36974273
correct.  you can download solaris for free from oracle.com. they charge for support only.bor you can go with an open source variation like nexenta, illuminos, opensolaris, etc..  nexenta is a server appliance variation which is both commercial or open source.  very easy to set up and use...

it also let's you create iscsi targets & nfs shares.  be sure to have a good JBOD controller on the HCL like LSI SAS/SATA.

ram improves read performance significantly.
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Author Comment

by:AdvNetSol
ID: 36974276
I have always stayed away from the integrated RAID support Microsoft offers.  Do you know of any problems with it that makes it unreliable?
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LVL 47

Assisted Solution

by:David
David earned 1500 total points
ID: 36974574
the msft integrated  raid is NOT appropriate for this config. don't use it.
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LVL 56

Assisted Solution

by:andyalder
andyalder earned 500 total points
ID: 36975829
So long as you backup the archive regularly why not just use JBOD? You've got to back it up anyway in case a virus wipes it all out and using individual disks limits the amount needed to restore if and when a disk fails. You would have to track what images are on what disk but presumably your software has some index for that anyway, it's not going to be practical to have everything in one huge folder.
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Author Comment

by:AdvNetSol
ID: 36976879
@andyalder - i agree.  Based upon information provided by dlethe's I had come to the conclusion that the best defense again data loss is to store archives on two separate systems with desktop class drives in a JBOD or all independently.  It is effective and keeps enough copies of the data that risk of complete loss is very slim.  I appriciate everyone's input on this, but will be awarding split points to both of you as your comments were all useful.
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Author Closing Comment

by:AdvNetSol
ID: 36976884
thank you both for your help.
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