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I just got a new (used) Mac Pro with an Apple raid card and 2 300GB 10k hard drives. I want to setup the 2 10k's in raid 0, but have a raid + 1 using two other drives (2 500gb 7200) to give me a 600GB raid 0+1 array using the 4 disks

My question is: Will using the slower (and bigger) drives for the mirrored part slow down the fast access given by the 2 10k drives? I figured that the mirrored drive is for writes only and that the internal write cache would handle it, but I am not sure.

EDIT
All 4 drives are SATA
2x300GB Western Digital Velociraptor 10,000 RPM drives
2x500GB Hitachi Deskstar 7200 RPM Drives

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Are those 300gb drives SAS drives? and the larger ones you want to add on are SATA drives? –  Troggy Oct 19 '09 at 19:14
    
I have edited the question with the answer to your question –  coneybeare Oct 19 '09 at 19:19

2 Answers 2

up vote 1 down vote accepted

I think you misunderstand how RAID 0+1 works. And you'll actually want to do 1+0, it performs the same, but is more fault tolerant in larger sets, so if you ever grow you'll have better protection.

RAID 0+1 isn't having a RAID 0 that's contents are mirrored to a separate RAID 1 automatically. In a 4 disk RAID 0+1 there are two RAID 0 sets that are then mirrored with eachother. In 1+0 there are pairs of RAID 1 mirrors that are then striped. In either RAID level, you lose 50% of the raw capacity.

In either case you are limited by the smallest size and speed. It sounds like what you may want to do is RAID 1 the 10k drives and create a separate RAID 1 out of the 7.2k drives and skip the striping.

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You are right. I dont need a 0 raid at all. The 2 10k drives in redundancy will be the fastest for me which is all I really care about. –  coneybeare Oct 19 '09 at 19:55

Usually people buy matched drives when using RAID. My guess is that 2 slow drives and 2 fast drives will give a performance that is somewhere inbetween 4 slow drives, and 4 fast drives.

One downside is that you'll be wasting 400GB of space, since the extra space on the larger drives will not be usable.

There is no distinction between drives in a mirror set, it's not like one is the main drive and one is the mirror drive, they are both used equally. Since you already have the drives, why not run a benchmark in both cases and see what speeds you get? There are too many variables for us to give you an accurate prediction of speed.

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I am ok with the wasted space. I am using this for a speed boost with redundancy only. I am trying to avoid buying 2 new 10k drives if possible, but it looks like I will have to to get the fastest speed out of this –  coneybeare Oct 19 '09 at 19:26

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