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It seems that certain MegaRAID chips don't support JBOD (unfortunately).

I've read online that to make these controllers act as a pass-through, I should configure the disks in RAID0.

What RAID0 settings do you recommend?

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Which MegaRAID are we talking about? –  Nils Nov 27 '11 at 20:34

6 Answers 6

up vote 2 down vote accepted

I run this exact setup. MegaCli has a useful option called something like CfgEachDskRaid0 which will configure every disk on the array as raid0, ensuring a consistent configuration.

It's not true that it's impossible to hot swap disks with this setup, although it is clunky to do so (especially because MegaCli itself is hardly a paragon of usability), basically involves deconfiguring the old raid array and reconfiguring a new one every time you want to swap a disk.

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thanks for hitting the point. So i have to install megacli on freebsd and i will sleep the night =) –  cedivad Nov 27 '11 at 18:17
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This is still a bad solution for long-term ZFS use. –  ewwhite Nov 27 '11 at 20:44

Are you trying to use the card for a software RAID solution like ZFS? Which controller are you using? If this is the case, using multiple RAID-0 logical drives will create an ugly situation if you need to swap a failed disk. The replacement drive will not be recognized until you reboot/reinitialize a new RAID-0 array containing the failed disk. It's not worth it. Use a proper HBA if possible, OR use the hardware RAID functions of the controller with ZFS (sometimes it makes sense).

Please refer to: ZFS SAS/SATA controller recommendations

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Exactly. I just finished to configure the 24 drives using megaraid's webios, a painful game. And yes, i will use ZFS. (i decided that 2 drives goes on raid 1 hardware for the os, the other are JBOD to ZFS). I'm using a 9280-4i4e, unfortunately i can't change it! –  cedivad Nov 27 '11 at 15:29
    
There's a big downside to configuring multiple RAID-0 arrays using the controller you're using (this also applies to Dell and HP RAID controllers). If you DO lose a disk, it's the same as losing a logical drive. Your replacement disk won't be recognized until your reboot. E.g. you won't have hot-swap capabilities. If you're interested in running a ZFS-based solution the right way, use one of the controllers I linked to in my earlier post. –  ewwhite Nov 27 '11 at 15:31
    
understood and received that i can't go this way. Thanks. –  cedivad Nov 27 '11 at 15:35
    
[given the impossibility to change the controller], please look at this page: kb.lsi.com/KnowledgebaseArticle16511.aspx - maybe the red text is the solutions to my problems? =) –  cedivad Nov 27 '11 at 16:02
    
Probably not. It's just a downtime risk. The system will run just fine. It just means you'll need a reboot if you have to replace a failed disk. That's all. –  ewwhite Nov 27 '11 at 16:06

Don't do this with 24 drives. Get a different controller. Anything based on the LSI 1068e (which is a bottom-of-the-line option for many Dell and IBM servers) will support JBOD. Dell calls it a SAS 6/iR and IBM calls it a ServeRAID BR10i.

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Point is that, even paying, i can't change my controller. It's an OVH HG server. I contacted the support to see if they can do an exception, but i'm not optimist. Thanks for the tip. –  cedivad Nov 27 '11 at 15:32

On our MegaRAID card we just make each drive its own raid-0 array, however we rarely have more than one drive in this configuration and I have no idea how well this scales.

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yes, it's the same thing i'm doing - let's hope it to work on 24 drives :( –  cedivad Nov 27 '11 at 13:24

Untrue! Some of the MegaRAID cards (such as the raid controller that IBM rebrands as the M1015) do support JBOD passthru.

If you want to use JBOD mode I'd suggest these cards. Know a local IBM VAR? I'd recommend getting friendly with them - odds are they have a whole mess of these cards on hand.

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Thanks, but i can't change my card! :( –  cedivad Nov 27 '11 at 15:29

Can`t you simply switch off the raid-controller in the BIOS?

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I wouldn't see any disk at all if I did so! –  cedivad Nov 27 '11 at 20:41
    
I will try, but I'm dubios it will work... I will report it –  cedivad Nov 28 '11 at 3:20
    
disabling boot from card is useless. –  cedivad Nov 28 '11 at 13:08
    
An actual server where this would have worked would have been a Dell PowerEdge 2850 with PERC5i raid-controller. This raid-controller is being activated by a key. If the key is not present it will serve the disks as JBOD. Thus there is an option (if the key is present) to disable raid - and you will have JBOD instead. But that does not seem to be the case with "your" server. –  Nils Nov 30 '11 at 20:37
    
It's a card inserted on the server, it's not an integrated stuff. thanks anyway. –  cedivad Dec 1 '11 at 13:07

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