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Running your OS off a mirrored Raid

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Nicholastoth
Running your OS off a mirrored Raid
on Sep 22, 2007 at 6:26:38 pm

So I'd like to comment that I know absolutely nothing about RAID terminology. But i was wondering if it would be intelligent to:

Raid 2 drives together for the main OS, mirrored to a backup drive. And run windows off a 10k Raptor. I literally just ordered the machine, and I need to fill it with space. Why is this a bad idea? Why is this a good idea?

Also, check out newegg.com for Mac Pro ram, its staggeringly cheap.


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Alan Okey
Re: Running your OS off a mirrored Raid
on Sep 27, 2007 at 9:41:24 pm

[Nicholastoth] "i was wondering if it would be intelligent to:

Raid 2 drives together for the main OS, mirrored to a backup drive. And run windows off a 10k Raptor."


First of all, read about RAID terminology. There's plenty of good information out there about RAID - educate yourself before you go any further.

Striping (RAID 0) spans data across two or more disks simultaneously to increase read/write speeds.

Mirroring (RAID 1) duplicates the same data on two volumes for redundancy in case one drive goes bad.

Higher level RAID numbers combine striping and data parity to deliver increased throughput as well as redundancy.

FYI: disks or partitions in a striped set need to be the same size. Disks, partitions or volumes in a mirrored pair need to be the same size.

It sounds like you are asking about using a striped disk pair (RAID 0) mirrored to a third drive (RAID 1) for your OS volume. This could work in theory, but I don't think it would be optimal to mirror a striped volume to a single drive. Read/write speed in such a configuration is most likely limited to the speed of the single drive in the mirror, negating the speed benefit of using a striped set.

You're probably more concerned with fast reads from an OS volume than fast writes, so you could configure two drives in a mirror (RAID 1) and select the "enable striped reads" option. This would allow you to benefit from both faster read access and redundancy, although write speed to a RAID 1 volume suffers a slight speed penalty compared to write speed to a non-RAID volume.

RAID 10 (two mirrored volumes striped together, needs a minimum of 4 disks) would ordinarily be a good option, but not in your case. Boot Camp won't work on OS X RAID partitions, so you're stuck with needing a single internal drive for Windows.

You could set up RAID 10 if you had three internal drives plus one external drive for OS X and a fourth internal drive for Windows.


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greg
Re: Running your OS off a mirrored Raid
by
on Sep 28, 2007 at 9:20:28 pm

Can I ask a follow up question.
I'm looking into using a simple mirrored RAID 1 setup for data storage on my mac. I had a drive crash recently and I got nervous... so any way, I'm looking at a Sonnet G5 jive expansion for internal drives... and I read on WD site that their Desktop Drives should Not be used in RAID. Other people have suggested that this isn't such a big deal, but I have been unable to get a clear read on this beyond WD's own info.

See it here.

Do you have a take on this? Something to worry about or not?


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