RAID Question

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RAID Question

Post by Fat_bloater_dave » Thu Feb 21, 2008 4:20 am

Hi Guys,

A quick question I've never used RAID before and was thinking about setting up a RAID array in a Homemade NAS box. from what ive read I'm thinking Raid 0 (its not gonna be very important data) But as i understand it if i use 4 disks that consist of 250GBx3 and a 500GB then i will only get 1TB instead of 1.25TB is there a RAID that lets you use diffrent sized disks and still use all of their size?

Thanks for any help


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Post by nutball » Thu Feb 21, 2008 5:17 am

Not RAID as such. What you're looking for is a JBOD setup (Just a Bunch Of Discs) with a logical volume manager (LVM) on top. This sort of thing is pretty trivial under Linux (Windows I dunno about). If you use the right file system you can even add discs later, expand the logical volume and grow the file system ... without reformatting or data loss.

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Post by nick705 » Thu Feb 21, 2008 5:23 am

I think you're confusing RAID 0 and RAID 5 (which has redundancy, hence why you can't use the full capacity). In any case, what you probably want is JBOD (Just a Bunch Of Disks), which lets you concatenate differently sized disks into one large volume. You still risk losing everything if one drive dies though.

I think personally I'd avoid RAID altogether and stick with individual drives, or else take a look at Windows Home Server which automatically pools your drives into one continuous storage space, but mounts each drive independently so there's no array to break, and they're individually accessible if the worst happens.

/edit: too slow, as usual... :roll:

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Post by Fat_bloater_dave » Thu Feb 21, 2008 6:01 am

Oh ok, thanks to both of you, I shall look into JBOD, i will be using Linux (Ubuntu) so i glad its easy under that.

Thanks again


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Post by sjoukew » Fri Feb 22, 2008 12:46 pm

raid explained on wikipedia. very good article .

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Post by angelkiller » Sat Feb 23, 2008 9:07 am

I'm in the planning phase of making a file server, and since we're all here I have some questions about the Logical Volume Manager nutball was referring to.

First, a LVM basically puts all the HDDs into one JBOD volume and you can stripe/mirrior different parts of the JBOD volume. Is my understanding correct?

Second, how reliable/redundant is a LVM mirroring solution? For example, let's say my JBOD volume totals to 400GB. I then decide to create a 20GB mirrored section. (So there will be two identical 20GB sections, using 40GB of space) My question is what if this virtual mirrored array is physically on the first HDD? If the first HDD crashes, won't I lose all my data even though it was in a virtual array? How would I create redundancy in case of a HDD failure?

Third, this is a completely software solution, right? So I would not configure my SATA adapter to any RAID format. The LVM will see (lets say) 4 HDDs and the OS will only see one. Or do I make a JBOD array with the SATA adapter and the LVM will create the striped/mirrored sections. Or do I have it completely wrong.

Sorry for the slight thread hijack :oops:

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