[NTLUG:Discuss] Re: looking for raid & controller advice -- "FRAID" card = "software RAID"

[Kevin Brannen]

Bryan J. Smith wrote:

>On Sat, 2004-12-04 at 15:06, Kevin Brannen wrote:
>  
>
> ...
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>>The 2 client machine control CD duplicators, but even burning at 48X 
>>shouldn't tax the file server.
>>    
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>
>Er, um, I don't recommend recording over a network.  I'd copy the .iso
>locally first.  It's worth the overhead in transfer time IMHO.
>  
>

If I build the file server, pulling from the file server to burn is 
probably the only "easy" way to make it work.  I'm just the visionary 
and sysadmin.  The people who do most of the burning work are not 
technical, and the burning software is not very sophisticated...sigh.

> ...
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>>If I were to go with 0+1, which I don't think I need, I'd have to get 
>>the -8 version of the card, because I want to be able to approach TB 
>>capacity over the next couple of years.  I've got almost 200GB now and 
>>am growing faster than planned, so I am concerned about size.
>>    
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>There's always the option to do what I do at home (on a 8-channel card):
>  2-disc RAID-1 System + 6-disc RAID-5 Data
>  
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Oh, you can logically split a card?  Hmm, you're going to have to stop 
giving me options; my head is going to explode! ;-)

>The big "performance hit" isn't so much the Data (which can vary), but
>the System filesystems like swap, /tmp, /var, etc...  You should _avoid_
>putting swap, /tmp and /var on RAID-5 if you can.
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The root & swap are on separate drives.  The RAID-5 is only for the data 
which must live.  Reinstalling the OS is child's play next to recreating 
the data (which can be done but is hideous to do, and I have to recreate 
about half of it because of the double drive failure).

>>Because of the reliability concerns, I'm thinking hard about doing 
>>RAID-5 with a hot-spare; which seems wasteful to me initially, until I 
>>remember that I've just lost 2 drives in the last week, and now will 
>>have to spend a day or more reloading images from old CDs.  Grrr!
>>    
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>Yes, hot spares are nice.  So is RAID-6 (two parity slices).
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The first step in my research was to refamiliarize myself with the RAID 
level definitions.  Six looked nice, but I've never seen its support in 
any of the cards I've been looking at, nor in Linux's Software RAID 
HowTo.  So it's just a theoretical thing to me at this time.

...

>>Also, if I were to go with the 9500S-8, I only see SATA versions.  I 
>>haven't heard any good SATA success stories on Linux yet.
>>    
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>Okay, this is where you seem to be missing something.
>
>With an "intelligent" RAID controller, the System/OS _never_ sees the
>storage controllers.  *NEVER*  The System/OS _only_ talks to the
>on-board intelligence, the ASIC in the case of 3Ware.  The ASIC is the
>_only_ thing that handles ATA transfers -- that's it!
>
>As such, you _never_ have ATA/SATA compatibility issues!  Because Linux
>_never_ talks to the on-board SATA controllers or drives!
>
>...
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OK, thanks for the explanation!

> ...
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>>Do the scales tip towards this setup (RAID-5 individually plus mirror 
>>between machines)?  Or towards the fileserver (RAID-5 plus HS)?  [While 
>>the file server would give me an opportunity for Linux advocacy, it's a 
>>fringe benefit and not the goal, so don't let that enter into the equation.]
>>    
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>Two, independent filesystems give you additional failover/redundancy.
>...
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Hmm, now you've got me leaning back the other way, because the file 
server does create a single point of failure, and I'm trying to minimize 
SPOFs (the reason I have 2 duplicators to begin with!).  I could put a 
7506-4LP or a 9800S-4LP in each system with 3 250G disks in RAID-5, 
mirroring to each other nightly.  That'll set me back about $800 or so a 
system, but that's within my budget.

Thanks!
Kevin