Mac pro non-paired drives RAID 0 array

[OracleRedux]

I currently have the following drives in my Mac Pro (Early 2008):
WD6400AAKS
WD7500AAKS
WD5000AAKS
Samsung HD203WI

The Caviar Blue drives were bought in the pre-Black era, back in Early 2008. Or at least they certainly hope so; I purchased the WD6400AAKS as the boot drive thinking it was the fastest 7K available at the time (BareFeats review (http://www.barefeats.com/harper14.html)).

I am about to install either an OCZ Vertex 2 or OWC Mercury Extreme Pro SSD in the optical drive bay.

I plan to re-purpose the 640, and either the 750 or 500, as a Software RAID 0 array (using Disk Utility), backed up using Time Machine / Super Duper. The third WD drive will be used for Boot Camp. The Samsung is a "green" Media Drive (although AJA has it currently matching the WD 640 in speed).
My intention is to improve the speed of access to user files etc, since a 60GB SSD is not big enough, nor suitable for my home folder.

I therefore ask; am I nuts? (I am aware of the increased risk of data loss)

My initial thought is that mismatched drives in a RAID 0 array may not result in the performance increase I am looking for. Apologies for the capitalisation error in the post title - wish I could edit it!

[nanofrog]

Yes, you can stripe mismatched drives. :)

What will happen, is both the speed and capacity will be affected by the smallest and slowest drive respectively in the set. So if you've a 500 and 750GB member, you'd get 2x 500GB = 1TB of usable capacity (additional 250GB on the 750 won't be accessible, unless you partition it in a 500/250 scheme, as you'd want the faster tracks for the stripe set).

Worst case performance will be n members * the slowest disk (likely what you'll see, as it's only a 2 member set, and the performance difference between the intended disks isn't likely to be that much, say a differential of 10MB/s or so).

So if the slowest drive is good for ~75MB/s, then 150MB/s is a realistic estimate of sustained throughputs (respective of read/write values you can locate from independent reviews).

Hope this helps. :)

[DoFoT9]

as per the scenario nano has outlined - you could use the remaining space to JBOD (or similar) it into a nice extra partition to muck around with :)

i have done something similar with my 4 drive RAID5 array.

so a striped RAID in your scenario would give 1.5TB total, and a 140GB + 250GB partition remaining - JBOD that into a 390GB extra partition and away you go!

[OracleRedux]

Thanks very much for both those replies, encouraging. To clear up any ambiguity; I only plan to stripe 2 drives. The third will be used for Windows under Boot Camp and as I understand it, one cannot have RAID on a Boot Camp drive.

How much of a performance hit does *software* RAID result in?

[Transporteur]

How much of a performance hit does *software* RAID result in?

Pretty close to n-times the performance of a single drive, with n being the amount of drives you put in a RAID 0 array.

This won't apply for access time and random access, though, only for sequential access.