Thread: raid pci card
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Old 6th June, 2005, 09:13 PM
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Originally Posted by krazefinn
2nd post here after lurking for months....does the third drive in a raid5 array also have to be equal size? Or should it be twice the size? offhand i would guess that if the first two, (say 80 g) drives are striped (into a 160), that third drive, to mirror the whole first pair, *should* be a 160 gig. Or is my cursory understanding impaired somehow? I'm also assuming that your raid card MUST officially support raid 5, or you are SOL, and furthermore, to avoid the master/slave slowdown (no concurrent read/writes on same channel) that one really requires a four channel...Thx for edifying me......
Sorry for not responding before now.

Eh, no. Err..yes. Umm.......what? Sorry, your question has really confused me.

In general, all drives in a RAID should be the same size, so if you currently have two drives that are 80G in a RAID0 or a RAID1, and you add a third drive, it should also be 80G. However, if you are adding the drive to an existing RAID1, then you will only be able to add the drive as a 'hot-spare', because RAID1 only works with 2 drives. For RAID0, depending on the controller, you may be able to build the drive into the array and expand the array, or you may have to flush all the data on the drives and reinitialize the array in the new configuration.

Not that I said 'in general'. If you have two 80G drives in a RAID and you can't get another 80G drive, but you do have a 160G drive, you can put the larger drive into the array, but you will only be able to use 80G of the storage space on the drive, unless your controller allows 'spanning' of dissimilar drives. I have only ever seen this done with a RAID0 configuration. Because of the way RAID works, I would be HIGHLY surprised if you could do it in any of the truly redundant modes (like RAID1 or RAID5).
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