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Old 07-19-2005, 07:48 PM   #1
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Help with RAID setup (dmraid)

Hi... I finally figured out that I can use 'dmraid' to see that my RAID0 stripe on a Silicon Image 0680 controller is actually active,

[root@val ~]# dmraid -r
/dev/hdb: sil, "sil_afahdcacccai", stripe, ok, 488393728 sectors, data@ 0
/dev/hdc: sil, "sil_afahdcacccai", stripe, ok, 488393728 sectors, data@ 0

The only problem is... I don't know how to create a partition on it! I can see that "/dev/md0" exists. Is that there for the stripe set referenced above? Once I manage to create a partition, I should be able to format the filesystem with 'mkfs'.

I think the tool I need is 'mdadm', but I cannot figure out what I need to do with it or if I should be pointing it at '/dev/md0'. Can somebody give me a clue?

Old 07-20-2005, 08:58 AM   #2
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I believe dmraid and mdadm are actually different tools which accomplish basically the same thing. I have not used dmraid, however, I can tell you how to use mdadm, which might be helpful.

To create a RAID-0 device, you should first create two partitions. In your case, this will probably be a partition covering the entire disk on hdb and hdc. You should change the type of each of these partitions to FD (Linux Software Raid Autodetect). Save your partition table and quit fdisk or whatever you used. You should now have /dev/hdb1 and /dev/hdc1.

Next, you need to instruct mdadm to create the array. You can do this with the command "mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/hdb1 /dev/hdc1". This will configure md0 to stripe across /dev/hdb1 and /dev/hdc1. Run "mdadm --detail /dev/md0" to see information about your array. You can now format the array using "mke2fs /dev/md0", and then mount it like you would any other file system.

It sounds like you'd rather use dmraid, so this may not be helpful, but it's good to know in any case.
Old 07-20-2005, 12:01 PM   #3
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Thanks for the reply... I think we were doing simultaneous/crossed posting or something, and I didn't see your reply before addming my previous one.

Anyway, that's good information to know about 'mdadm'. However, based on what you say and what I've learned in the meantime, I believe that tool is more aimed at having Linux do ALL of the RAID configuration and management... in fact, the equivalent of a completely software RAID solution.

In my case, the hardware card actually handles the maintenance of the stripe (or mirror) partially in hardware, with some of it being in software. I know very little about where to draw the line between those two parts of it, but I believe this should perform somewhat better than having the OS do all of the RAID management. For controllers of this type, 'dmraid' appears to be the tool to use.




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